Spring Framework Reference Documentation

4.1.0.RELEASE

Rod Johnson , Juergen Hoeller , Keith Donald , Colin Sampaleanu , Rob Harrop , Thomas Risberg , Alef

Arendsen , Darren Davison , Dmitriy Kopylenko , Mark Pollack , Thierry Templier , Erwin Vervaet , Portia

Tung , Ben Hale , Adrian Colyer , John Lewis , Costin Leau , Mark Fisher , Sam Brannen , Ramnivas

Laddad , Arjen Poutsma , Chris Beams , Tareq Abedrabbo , Andy Clement , Dave Syer , Oliver Gierke ,

Rossen Stoyanchev , Phillip Webb , Rob Winch , Brian Clozel , Stephane Nicoll , Sebastien Deleuze

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee

for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework iii

Table of Contents

I. Overview of Spring Framework ................................................................................................ 1

1. Getting Started With Spring ............................................................................................ 2

2. Introduction to Spring Framework .................................................................................... 3

2.1. Dependency Injection and Inversion of Control ...................................................... 3

2.2. Modules .............................................................................................................. 3

Core Container .................................................................................................. 4

AOP and Instrumentation ................................................................................... 5

Messaging ......................................................................................................... 5

Data Access/Integration ...................................................................................... 5

Web .................................................................................................................. 5

Test ................................................................................................................... 6

2.3. Usage scenarios ................................................................................................. 6

Dependency Management and Naming Conventions ............................................ 9

Spring Dependencies and Depending on Spring .......................................... 9

Maven Dependency Management ............................................................. 10

Maven "Bill Of Materials" Dependency ....................................................... 10

Gradle Dependency Management ............................................................. 11

Ivy Dependency Management ................................................................... 11

Distribution Zip Files ................................................................................. 12

Logging ............................................................................................................ 12

Not Using Commons Logging ................................................................... 12

Using SLF4J ............................................................................................ 13

Using Log4J ............................................................................................. 14

II. What’s New in Spring Framework 4.x .................................................................................... 16

3. New Features and Enhancements in Spring Framework 4.0 ............................................ 17

3.1. Improved Getting Started Experience .................................................................. 17

3.2. Removed Deprecated Packages and Methods .................................................... 17

3.3. Java 8 (as well as 6 and 7) ............................................................................... 17

3.4. Java EE 6 and 7 ............................................................................................... 18

3.5. Groovy Bean Definition DSL .............................................................................. 18

3.6. Core Container Improvements ............................................................................ 18

3.7. General Web Improvements ............................................................................... 19

3.8. WebSocket, SockJS, and STOMP Messaging ..................................................... 19

3.9. Testing Improvements ........................................................................................ 20

4. New Features and Enhancements in Spring Framework 4.1 ............................................ 21

4.1. JMS Improvements ............................................................................................ 21

4.2. Caching Improvements ...................................................................................... 21

4.3. Web Improvements ............................................................................................ 22

4.4. WebSocket STOMP Messaging Improvements .................................................... 23

4.5. Testing Improvements ........................................................................................ 23

III. Core Technologies .............................................................................................................. 25

5. The IoC container ........................................................................................................ 26

5.1. Introduction to the Spring IoC container and beans .............................................. 26

5.2. Container overview ............................................................................................ 26

Configuration metadata ..................................................................................... 27

Instantiating a container .................................................................................... 28

Composing XML-based configuration metadata .......................................... 29

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework iv

Using the container .......................................................................................... 30

5.3. Bean overview ................................................................................................... 30

Naming beans .................................................................................................. 31

Aliasing a bean outside the bean definition ................................................ 32

Instantiating beans ........................................................................................... 33

Instantiation with a constructor .................................................................. 33

Instantiation with a static factory method .................................................... 34

Instantiation using an instance factory method ........................................... 34

5.4. Dependencies ................................................................................................... 35

Dependency injection ....................................................................................... 35

Constructor-based dependency injection .................................................... 36

Setter-based dependency injection ............................................................ 38

Dependency resolution process ................................................................. 39

Examples of dependency injection ............................................................. 40

Dependencies and configuration in detail ........................................................... 42

Straight values (primitives, Strings, and so on) ........................................... 42

References to other beans (collaborators) .................................................. 43

Inner beans .............................................................................................. 44

Collections ............................................................................................... 44

Null and empty string values ..................................................................... 47

XML shortcut with the p-namespace .......................................................... 47

XML shortcut with the c-namespace .......................................................... 48

Compound property names ....................................................................... 49

Using depends-on ............................................................................................ 50

Lazy-initialized beans ....................................................................................... 50

Autowiring collaborators .................................................................................... 51

Limitations and disadvantages of autowiring ............................................... 52

Excluding a bean from autowiring .............................................................. 52

Method injection ............................................................................................... 53

Lookup method injection ........................................................................... 54

Arbitrary method replacement ................................................................... 55

5.5. Bean scopes ..................................................................................................... 56

The singleton scope ......................................................................................... 57

The prototype scope ......................................................................................... 58

Singleton beans with prototype-bean dependencies ............................................ 59

Request, session, and global session scopes .................................................... 59

Initial web configuration ............................................................................ 59

Request scope ......................................................................................... 60

Session scope .......................................................................................... 60

Global session scope ............................................................................... 60

Application scope ..................................................................................... 61

Scoped beans as dependencies ................................................................ 61

Custom scopes ................................................................................................ 63

Creating a custom scope .......................................................................... 63

Using a custom scope .............................................................................. 64

5.6. Customizing the nature of a bean ....................................................................... 65

Lifecycle callbacks ............................................................................................ 65

Initialization callbacks ............................................................................... 66

Destruction callbacks ................................................................................ 66

Default initialization and destroy methods .................................................. 67

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework v

Combining lifecycle mechanisms ............................................................... 68

Startup and shutdown callbacks ................................................................ 69

Shutting down the Spring IoC container gracefully in non-web applications

................................................................................................................. 70

ApplicationContextAware and BeanNameAware ................................................. 71

Other Aware interfaces ..................................................................................... 72

5.7. Bean definition inheritance ................................................................................. 73

5.8. Container Extension Points ................................................................................ 74

Customizing beans using a BeanPostProcessor ................................................. 74

Example: Hello World, BeanPostProcessor-style ........................................ 76

Example: The RequiredAnnotationBeanPostProcessor ............................... 77

Customizing configuration metadata with a BeanFactoryPostProcessor ................ 77

Example: the Class name substitution PropertyPlaceholderConfigurer .......... 78

Example: the PropertyOverrideConfigurer .................................................. 80

Customizing instantiation logic with a FactoryBean ............................................. 81

5.9. Annotation-based container configuration ............................................................ 81

@Required ....................................................................................................... 82

@Autowired ..................................................................................................... 83

Fine-tuning annotation-based autowiring with qualifiers ....................................... 86

Using generics as autowiring qualifiers .............................................................. 90

CustomAutowireConfigurer ................................................................................ 91

@Resource ...................................................................................................... 91

@PostConstruct and @PreDestroy .................................................................... 93

5.10. Classpath scanning and managed components ................................................. 93

@Component and further stereotype annotations ............................................... 93

Meta-annotations .............................................................................................. 94

Automatically detecting classes and registering bean definitions .......................... 94

Using filters to customize scanning ................................................................... 96

Defining bean metadata within components ....................................................... 97

Naming autodetected components ..................................................................... 98

Providing a scope for autodetected components ................................................ 99

Providing qualifier metadata with annotations ................................................... 100

5.11. Using JSR 330 Standard Annotations ............................................................. 101

Dependency Injection with @Inject and @Named ............................................. 101

@Named: a standard equivalent to the @Component annotation ....................... 101

Limitations of the standard approach ............................................................... 102

5.12. Java-based container configuration ................................................................. 103

Basic concepts: @Bean and @Configuration ................................................... 103

Instantiating the Spring container using AnnotationConfigApplicationContext ....... 104

Simple construction ................................................................................ 104

Building the container programmatically using register(Class<?>…) ........... 105

Enabling component scanning with scan(String…) .................................... 105

Support for web applications with AnnotationConfigWebApplicationContext

............................................................................................................... 106

Using the @Bean annotation .......................................................................... 107

Declaring a bean .................................................................................... 107

Receiving lifecycle callbacks ................................................................... 107

Specifying bean scope ............................................................................ 108

Customizing bean naming ....................................................................... 109

Bean aliasing ......................................................................................... 109

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework vi

Bean description ..................................................................................... 110

Using the @Configuration annotation ............................................................... 110

Injecting inter-bean dependencies ............................................................ 110

Lookup method injection ......................................................................... 111

Further information about how Java-based configuration works internally .... 111

Composing Java-based configurations ............................................................. 112

Using the @Import annotation ................................................................. 112

Conditionally including @Configuration classes or @Beans ....................... 116

Combining Java and XML configuration ................................................... 116

5.13. Environment abstraction ................................................................................. 118

Bean definition profiles ................................................................................... 119

@Profile ................................................................................................. 120

XML Bean definition profiles ............................................................................ 121

Enabling a profile ................................................................................... 122

Default profile ......................................................................................... 122

PropertySource Abstraction ............................................................................. 122

@PropertySource ........................................................................................... 123

Placeholder resolution in statements ................................................................ 124

5.14. Registering a LoadTimeWeaver ...................................................................... 124

5.15. Additional Capabilities of the ApplicationContext .............................................. 125

Internationalization using MessageSource ........................................................ 125

Standard and Custom Events .......................................................................... 128

Convenient access to low-level resources ........................................................ 131

Convenient ApplicationContext instantiation for web applications ....................... 132

Deploying a Spring ApplicationContext as a Java EE RAR file ........................... 132

5.16. The BeanFactory ........................................................................................... 133

BeanFactory or ApplicationContext? ................................................................ 133

Glue code and the evil singleton ..................................................................... 134

6. Resources .................................................................................................................. 136

6.1. Introduction ..................................................................................................... 136

6.2. The Resource interface .................................................................................... 136

6.3. Built-in Resource implementations .................................................................... 137

UrlResource ................................................................................................... 137

ClassPathResource ........................................................................................ 137

FileSystemResource ....................................................................................... 138

ServletContextResource .................................................................................. 138

InputStreamResource ..................................................................................... 138

ByteArrayResource ......................................................................................... 138

6.4. The ResourceLoader ....................................................................................... 138

6.5. The ResourceLoaderAware interface ................................................................ 139

6.6. Resources as dependencies ............................................................................. 140

6.7. Application contexts and Resource paths .......................................................... 140

Constructing application contexts ..................................................................... 140

Constructing ClassPathXmlApplicationContext instances - shortcuts .......... 141

Wildcards in application context constructor resource paths ............................... 141

Ant-style Patterns ................................................................................... 142

The Classpath*: portability classpath*: prefix ............................................ 142

Other notes relating to wildcards ............................................................. 143

FileSystemResource caveats .......................................................................... 143

7. Validation, Data Binding, and Type Conversion ............................................................ 145

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework vii

7.1. Introduction ..................................................................................................... 145

7.2. Validation using Spring’s Validator interface ...................................................... 145

7.3. Resolving codes to error messages .................................................................. 147

7.4. Bean manipulation and the BeanWrapper ......................................................... 148

Setting and getting basic and nested properties ............................................... 148

Built-in PropertyEditor implementations ............................................................ 150

Registering additional custom PropertyEditors .......................................... 153

7.5. Spring Type Conversion ................................................................................... 155

Converter SPI ................................................................................................ 155

ConverterFactory ............................................................................................ 156

GenericConverter ........................................................................................... 156

ConditionalGenericConverter ................................................................... 157

ConversionService API ................................................................................... 157

Configuring a ConversionService ..................................................................... 158

Using a ConversionService programmatically ................................................... 159

7.6. Spring Field Formatting .................................................................................... 159

Formatter SPI ................................................................................................. 160

Annotation-driven Formatting ........................................................................... 161

Format Annotation API ............................................................................ 162

FormatterRegistry SPI ..................................................................................... 162

FormatterRegistrar SPI ................................................................................... 163

Configuring Formatting in Spring MVC ............................................................. 163

7.7. Configuring a global date & time format ............................................................ 165

7.8. Spring Validation ............................................................................................. 166

Overview of the JSR-303 Bean Validation API ................................................. 166

Configuring a Bean Validation Provider ............................................................ 167

Injecting a Validator ................................................................................ 167

Configuring Custom Constraints .............................................................. 168

Spring-driven Method Validation .............................................................. 168

Additional Configuration Options .............................................................. 169

Configuring a DataBinder ................................................................................ 169

Spring MVC 3 Validation ................................................................................. 169

Triggering @Controller Input Validation .................................................... 169

Configuring a Validator for use by Spring MVC ......................................... 170

Configuring a JSR-303/JSR-349 Validator for use by Spring MVC .............. 170

8. Spring Expression Language (SpEL) ........................................................................... 172

8.1. Introduction ..................................................................................................... 172

8.2. Feature Overview ............................................................................................ 172

8.3. Expression Evaluation using Spring’s Expression Interface ................................. 173

The EvaluationContext interface ...................................................................... 175

Type Conversion .................................................................................... 175

Parser configuration ........................................................................................ 176

SpEL compilation ............................................................................................ 176

Compiler configuration ............................................................................ 177

Compiler limitations ................................................................................ 178

8.4. Expression support for defining bean definitions ................................................ 178

XML based configuration ................................................................................ 178

Annotation-based configuration ........................................................................ 179

8.5. Language Reference ........................................................................................ 180

Literal expressions .......................................................................................... 180

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework viii

Properties, Arrays, Lists, Maps, Indexers ......................................................... 180

Inline lists ....................................................................................................... 181

Inline Maps .................................................................................................... 181

Array construction ........................................................................................... 182

Methods ......................................................................................................... 182

Operators ....................................................................................................... 182

Relational operators ................................................................................ 182

Logical operators .................................................................................... 183

Mathematical operators ........................................................................... 183

Assignment .................................................................................................... 184

Types ............................................................................................................. 184

Constructors ................................................................................................... 184

Variables ........................................................................................................ 184

The #this and #root variables .................................................................. 185

Functions ....................................................................................................... 185

Bean references ............................................................................................. 185

Ternary Operator (If-Then-Else) ....................................................................... 186

The Elvis Operator ......................................................................................... 186

Safe Navigation operator ................................................................................ 186

Collection Selection ........................................................................................ 187

Collection Projection ....................................................................................... 187

Expression templating ..................................................................................... 188

8.6. Classes used in the examples .......................................................................... 188

9. Aspect Oriented Programming with Spring ................................................................... 192

9.1. Introduction ..................................................................................................... 192

AOP concepts ................................................................................................ 192

Spring AOP capabilities and goals ................................................................... 194

AOP Proxies .................................................................................................. 195

9.2. @AspectJ support ........................................................................................... 195

Enabling @AspectJ Support ............................................................................ 195

Enabling @AspectJ Support with Java configuration ................................. 195

Enabling @AspectJ Support with XML configuration ................................. 196

Declaring an aspect ........................................................................................ 196

Declaring a pointcut ........................................................................................ 197

Supported Pointcut Designators .............................................................. 197

Combining pointcut expressions .............................................................. 199

Sharing common pointcut definitions ........................................................ 199

Examples ............................................................................................... 201

Writing good pointcuts ............................................................................ 203

Declaring advice ............................................................................................. 204

Before advice ......................................................................................... 204

After returning advice .............................................................................. 204

After throwing advice .............................................................................. 205

After (finally) advice ................................................................................ 206

Around advice ........................................................................................ 206

Advice parameters .................................................................................. 207

Advice ordering ...................................................................................... 210

Introductions ................................................................................................... 211

Aspect instantiation models ............................................................................. 211

Example ......................................................................................................... 212

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework ix

9.3. Schema-based AOP support ............................................................................ 214

Declaring an aspect ........................................................................................ 214

Declaring a pointcut ........................................................................................ 215

Declaring advice ............................................................................................. 216

Before advice ......................................................................................... 216

After returning advice .............................................................................. 217

After throwing advice .............................................................................. 217

After (finally) advice ................................................................................ 218

Around advice ........................................................................................ 218

Advice parameters .................................................................................. 219

Advice ordering ...................................................................................... 220

Introductions ................................................................................................... 221

Aspect instantiation models ............................................................................. 221

Advisors ......................................................................................................... 221

Example ......................................................................................................... 222

9.4. Choosing which AOP declaration style to use .................................................... 224

Spring AOP or full AspectJ? ........................................................................... 224

@AspectJ or XML for Spring AOP? ................................................................. 225

9.5. Mixing aspect types ......................................................................................... 225

9.6. Proxying mechanisms ...................................................................................... 226

Understanding AOP proxies ............................................................................ 227

9.7. Programmatic creation of @AspectJ Proxies ..................................................... 229

9.8. Using AspectJ with Spring applications ............................................................. 229

Using AspectJ to dependency inject domain objects with Spring ........................ 230

Unit testing @Configurable objects .......................................................... 232

Working with multiple application contexts ................................................ 232

Other Spring aspects for AspectJ .................................................................... 233

Configuring AspectJ aspects using Spring IoC ................................................. 233

Load-time weaving with AspectJ in the Spring Framework ................................. 234

A first example ....................................................................................... 235

Aspects .................................................................................................. 237

META-INF/aop.xml ................................................................................. 238

Required libraries (JARS) ........................................................................ 238

Spring configuration ................................................................................ 238

Environment-specific configuration ........................................................... 241

9.9. Further Resources ........................................................................................... 242

10. Spring AOP APIs ...................................................................................................... 243

10.1. Introduction .................................................................................................... 243

10.2. Pointcut API in Spring .................................................................................... 243

Concepts ........................................................................................................ 243

Operations on pointcuts .................................................................................. 244

AspectJ expression pointcuts .......................................................................... 244

Convenience pointcut implementations ............................................................ 244

Static pointcuts ....................................................................................... 244

Dynamic pointcuts .................................................................................. 245

Pointcut superclasses ..................................................................................... 246

Custom pointcuts ............................................................................................ 246

10.3. Advice API in Spring ...................................................................................... 246

Advice lifecycles ............................................................................................. 246

Advice types in Spring .................................................................................... 246

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework x

Interception around advice ...................................................................... 246

Before advice ......................................................................................... 247

Throws advice ........................................................................................ 248

After Returning advice ............................................................................ 249

Introduction advice .................................................................................. 250

10.4. Advisor API in Spring ..................................................................................... 252

10.5. Using the ProxyFactoryBean to create AOP proxies ......................................... 252

Basics ............................................................................................................ 252

JavaBean properties ....................................................................................... 253

JDK- and CGLIB-based proxies ...................................................................... 254

Proxying interfaces ......................................................................................... 254

Proxying classes ............................................................................................ 256

Using global advisors ...................................................................................... 257

10.6. Concise proxy definitions ................................................................................ 257

10.7. Creating AOP proxies programmatically with the ProxyFactory .......................... 258

10.8. Manipulating advised objects .......................................................................... 259

10.9. Using the "auto-proxy" facility ......................................................................... 260

Autoproxy bean definitions .............................................................................. 260

BeanNameAutoProxyCreator ................................................................... 260

DefaultAdvisorAutoProxyCreator .............................................................. 261

AbstractAdvisorAutoProxyCreator ............................................................ 262

Using metadata-driven auto-proxying ............................................................... 262

10.10. Using TargetSources .................................................................................... 264

Hot swappable target sources ......................................................................... 264

Pooling target sources .................................................................................... 264

Prototype target sources ................................................................................. 266

ThreadLocal target sources ............................................................................. 266

10.11. Defining new Advice types ............................................................................ 266

10.12. Further resources ......................................................................................... 267

11. Testing ..................................................................................................................... 268

11.1. Introduction to Spring Testing ......................................................................... 268

11.2. Unit Testing ................................................................................................... 268

Mock Objects ................................................................................................. 268

Environment ........................................................................................... 268

JNDI ...................................................................................................... 268

Servlet API ............................................................................................. 268

Portlet API ............................................................................................. 268

Unit Testing support Classes .......................................................................... 269

General utilities ...................................................................................... 269

Spring MVC ........................................................................................... 269

11.3. Integration Testing ......................................................................................... 269

Overview ........................................................................................................ 269

Goals of Integration Testing ............................................................................ 270

Context management and caching ........................................................... 270

Dependency Injection of test fixtures ....................................................... 270

Transaction management ........................................................................ 271

Support classes for integration testing ..................................................... 271

JDBC Testing Support .................................................................................... 272

Annotations .................................................................................................... 272

Spring Testing Annotations ..................................................................... 272

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xi

Standard Annotation Support .................................................................. 278

Spring JUnit Testing Annotations ............................................................. 279

Meta-Annotation Support for Testing ........................................................ 280

Spring TestContext Framework ....................................................................... 281

Key abstractions ..................................................................................... 282

TestExecutionListener configuration ......................................................... 283

Context management .............................................................................. 285

Dependency injection of test fixtures ........................................................ 304

Testing request and session scoped beans .............................................. 306

Transaction management ........................................................................ 308

Executing SQL scripts ............................................................................ 312

TestContext Framework support classes .................................................. 316

Spring MVC Test Framework .......................................................................... 318

Server-Side Tests ................................................................................... 319

Client-Side REST Tests .......................................................................... 324

PetClinic Example .......................................................................................... 324

11.4. Further Resources ......................................................................................... 326

IV. Data Access ..................................................................................................................... 327

12. Transaction Management .......................................................................................... 328

12.1. Introduction to Spring Framework transaction management .............................. 328

12.2. Advantages of the Spring Framework’s transaction support model ..................... 328

Global transactions ......................................................................................... 328

Local transactions ........................................................................................... 329

Spring Framework’s consistent programming model ......................................... 329

12.3. Understanding the Spring Framework transaction abstraction ............................ 330

12.4. Synchronizing resources with transactions ....................................................... 333

High-level synchronization approach ................................................................ 333

Low-level synchronization approach ................................................................. 334

TransactionAwareDataSourceProxy ................................................................. 334

12.5. Declarative transaction management ............................................................... 334

Understanding the Spring Framework’s declarative transaction implementation ... 336

Example of declarative transaction implementation ........................................... 336

Rolling back a declarative transaction .............................................................. 340

Configuring different transactional semantics for different beans ........................ 341

<tx:advice/> settings ....................................................................................... 343

Using @Transactional ..................................................................................... 344

@Transactional settings .......................................................................... 349

Multiple Transaction Managers with @Transactional ................................. 350

Custom shortcut annotations ................................................................... 351

Transaction propagation .................................................................................. 351

Required ................................................................................................ 351

RequiresNew .......................................................................................... 352

Nested ................................................................................................... 352

Advising transactional operations ..................................................................... 352

Using @Transactional with AspectJ ................................................................. 355

12.6. Programmatic transaction management ........................................................... 356

Using the TransactionTemplate ....................................................................... 356

Specifying transaction settings ................................................................ 358

Using the PlatformTransactionManager ............................................................ 358

12.7. Choosing between programmatic and declarative transaction management ........ 359

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xii

12.8. Application server-specific integration .............................................................. 359

IBM WebSphere ............................................................................................. 359

Oracle WebLogic Server ................................................................................. 359

12.9. Solutions to common problems ....................................................................... 360

Use of the wrong transaction manager for a specific DataSource ....................... 360

12.10. Further Resources ....................................................................................... 360

13. DAO support ............................................................................................................ 361

13.1. Introduction .................................................................................................... 361

13.2. Consistent exception hierarchy ....................................................................... 361

13.3. Annotations used for configuring DAO or Repository classes ............................ 362

14. Data access with JDBC ............................................................................................ 364

14.1. Introduction to Spring Framework JDBC .......................................................... 364

Choosing an approach for JDBC database access ........................................... 364

Package hierarchy .......................................................................................... 365

14.2. Using the JDBC core classes to control basic JDBC processing and error

handling ................................................................................................................. 366

JdbcTemplate ................................................................................................. 366

Examples of JdbcTemplate class usage ................................................... 366

JdbcTemplate best practices ................................................................... 368

NamedParameterJdbcTemplate ....................................................................... 370

SQLExceptionTranslator .................................................................................. 372

Executing statements ...................................................................................... 373

Running queries ............................................................................................. 374

Updating the database .................................................................................... 375

Retrieving auto-generated keys ....................................................................... 375

14.3. Controlling database connections .................................................................... 375

DataSource .................................................................................................... 375

DataSourceUtils .............................................................................................. 377

SmartDataSource ........................................................................................... 377

AbstractDataSource ........................................................................................ 377

SingleConnectionDataSource .......................................................................... 377

DriverManagerDataSource .............................................................................. 377

TransactionAwareDataSourceProxy ................................................................. 378

DataSourceTransactionManager ...................................................................... 378

NativeJdbcExtractor ........................................................................................ 378

14.4. JDBC batch operations .................................................................................. 379

Basic batch operations with the JdbcTemplate ................................................. 379

Batch operations with a List of objects ............................................................. 380

Batch operations with multiple batches ............................................................ 381

14.5. Simplifying JDBC operations with the SimpleJdbc classes ................................ 381

Inserting data using SimpleJdbcInsert .............................................................. 382

Retrieving auto-generated keys using SimpleJdbcInsert .................................... 382

Specifying columns for a SimpleJdbcInsert ...................................................... 383

Using SqlParameterSource to provide parameter values ................................... 384

Calling a stored procedure with SimpleJdbcCall ............................................... 384

Explicitly declaring parameters to use for a SimpleJdbcCall ............................... 386

How to define SqlParameters .......................................................................... 387

Calling a stored function using SimpleJdbcCall ................................................. 387

Returning ResultSet/REF Cursor from a SimpleJdbcCall ................................... 388

14.6. Modeling JDBC operations as Java objects ..................................................... 389

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xiii

SqlQuery ........................................................................................................ 389

MappingSqlQuery ........................................................................................... 390

SqlUpdate ...................................................................................................... 391

StoredProcedure ............................................................................................. 391

14.7. Common problems with parameter and data value handling .............................. 394

Providing SQL type information for parameters ................................................. 394

Handling BLOB and CLOB objects .................................................................. 395

Passing in lists of values for IN clause ............................................................ 396

Handling complex types for stored procedure calls ........................................... 396

14.8. Embedded database support .......................................................................... 397

Why use an embedded database? .................................................................. 398

Creating an embedded database instance using Spring XML ............................ 398

Creating an embedded database instance programmatically .............................. 398

Extending the embedded database support ...................................................... 398

Using HSQL ................................................................................................... 398

Using H2 ........................................................................................................ 398

Using Derby ................................................................................................... 399

Testing data access logic with an embedded database ..................................... 399

14.9. Initializing a DataSource ................................................................................. 399

Initializing a database instance using Spring XML ............................................. 399

Initialization of Other Components that Depend on the Database ............... 400

15. Object Relational Mapping (ORM) Data Access .......................................................... 402

15.1. Introduction to ORM with Spring ..................................................................... 402

15.2. General ORM integration considerations ......................................................... 403

Resource and transaction management ........................................................... 403

Exception translation ....................................................................................... 404

15.3. Hibernate ....................................................................................................... 404

SessionFactory setup in a Spring container ...................................................... 404

Implementing DAOs based on plain Hibernate 3 API ........................................ 405

Declarative transaction demarcation ................................................................ 406

Programmatic transaction demarcation ............................................................ 408

Transaction management strategies ................................................................ 409

Comparing container-managed and locally defined resources ............................ 411

Spurious application server warnings with Hibernate ......................................... 412

15.4. JDO .............................................................................................................. 413

PersistenceManagerFactory setup ................................................................... 413

Implementing DAOs based on the plain JDO API ............................................. 414

Transaction management ................................................................................ 416

JdoDialect ...................................................................................................... 417

15.5. JPA ............................................................................................................... 417

Three options for JPA setup in a Spring environment ........................................ 417

LocalEntityManagerFactoryBean .............................................................. 417

Obtaining an EntityManagerFactory from JNDI ......................................... 418

LocalContainerEntityManagerFactoryBean ............................................... 418

Dealing with multiple persistence units ..................................................... 420

Implementing DAOs based on plain JPA .......................................................... 421

Transaction Management ................................................................................ 423

JpaDialect ...................................................................................................... 423

16. Marshalling XML using O/X Mappers ......................................................................... 425

16.1. Introduction .................................................................................................... 425

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xiv

Ease of configuration ...................................................................................... 425

Consistent Interfaces ...................................................................................... 425

Consistent Exception Hierarchy ....................................................................... 425

16.2. Marshaller and Unmarshaller .......................................................................... 425

Marshaller ...................................................................................................... 425

Unmarshaller .................................................................................................. 426

XmlMappingException ..................................................................................... 427

16.3. Using Marshaller and Unmarshaller ................................................................. 427

16.4. XML Schema-based Configuration .................................................................. 429

16.5. JAXB ............................................................................................................. 429

Jaxb2Marshaller ............................................................................................. 429

XML Schema-based Configuration ........................................................... 430

16.6. Castor ........................................................................................................... 430

CastorMarshaller ............................................................................................ 430

Mapping ......................................................................................................... 431

XML Schema-based Configuration ........................................................... 431

16.7. XMLBeans ..................................................................................................... 432

XmlBeansMarshaller ....................................................................................... 432

XML Schema-based Configuration ........................................................... 432

16.8. JiBX .............................................................................................................. 432

JibxMarshaller ................................................................................................ 433

XML Schema-based Configuration ........................................................... 433

16.9. XStream ........................................................................................................ 433

XStreamMarshaller ......................................................................................... 433

V. The Web ........................................................................................................................... 435

17. Web MVC framework ................................................................................................ 436

17.1. Introduction to Spring Web MVC framework .................................................... 436

Features of Spring Web MVC ......................................................................... 436

Pluggability of other MVC implementations ...................................................... 438

17.2. The DispatcherServlet .................................................................................... 438

Special Bean Types In the WebApplicationContext ........................................... 441

Default DispatcherServlet Configuration ........................................................... 442

DispatcherServlet Processing Sequence .......................................................... 442

17.3. Implementing Controllers ................................................................................ 444

Defining a controller with @Controller .............................................................. 444

Mapping Requests With @RequestMapping ..................................................... 445

@Controller's and AOP Proxying ......................................................... 446

New Support Classes for @RequestMapping methods in Spring MVC 3.1 .. 446

URI Template Patterns ........................................................................... 447

URI Template Patterns with Regular Expressions ..................................... 448

Path Patterns ......................................................................................... 449

Path Pattern Comparison ........................................................................ 449

Path Patterns with Placeholders .............................................................. 449

Path Pattern Matching By Suffix .............................................................. 449

Matrix Variables ...................................................................................... 449

Consumable Media Types ....................................................................... 451

Producible Media Types .......................................................................... 451

Request Parameters and Header Values ................................................. 452

Defining @RequestMapping handler methods .................................................. 452

Supported method argument types .......................................................... 453

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xv

Supported method return types ............................................................... 455

Binding request parameters to method parameters with @RequestParam ... 456

Mapping the request body with the @RequestBody annotation .................. 456

Mapping the response body with the @ResponseBody annotation ............. 457

Creating REST Controllers with the @RestController annotation ................ 458

Using HttpEntity ...................................................................................... 458

Using @ModelAttribute on a method ....................................................... 458

Using @ModelAttribute on a method argument ......................................... 459

Using @SessionAttributes to store model attributes in the HTTP session

between requests ................................................................................... 461

Specifying redirect and flash attributes ..................................................... 461

Working with "application/x-www-form-urlencoded" data ............................ 462

Mapping cookie values with the @CookieValue annotation ........................ 463

Mapping request header attributes with the @RequestHeader annotation ... 463

Method Parameters And Type Conversion ............................................... 463

Customizing WebDataBinder initialization ................................................. 464

Support for the Last-Modified Response Header To Facilitate Content

Caching ................................................................................................. 465

Advising controllers with the @ControllerAdvice annotation ................. 465

Jackson Serialization View Support ......................................................... 466

Jackson JSONP Support ........................................................................ 466

Asynchronous Request Processing .................................................................. 467

Exception Handling for Async Requests ................................................... 468

Intercepting Async Requests ................................................................... 468

Configuration for Async Request Processing ............................................ 469

Testing Controllers ......................................................................................... 470

17.4. Handler mappings .......................................................................................... 470

Intercepting requests with a HandlerInterceptor ................................................ 471

17.5. Resolving views ............................................................................................. 473

Resolving views with the ViewResolver interface .............................................. 473

Chaining ViewResolvers ................................................................................. 475

Redirecting to views ....................................................................................... 475

RedirectView .......................................................................................... 476

The redirect: prefix ................................................................................. 476

The forward: prefix ................................................................................. 477

ContentNegotiatingViewResolver ..................................................................... 477

17.6. Using flash attributes ..................................................................................... 479

17.7. Building URIs ................................................................................................. 480

Building URIs to Controllers and methods ........................................................ 481

Building URIs to Controllers and methods from views ....................................... 481

17.8. Using locales ................................................................................................. 482

Obtaining Time Zone Information .................................................................... 482

AcceptHeaderLocaleResolver .......................................................................... 483

CookieLocaleResolver ..................................................................................... 483

SessionLocaleResolver ................................................................................... 483

LocaleChangeInterceptor ................................................................................ 483

17.9. Using themes ................................................................................................ 484

Overview of themes ........................................................................................ 484

Defining themes ............................................................................................. 484

Theme resolvers ............................................................................................. 485

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xvi

17.10. Spring’s multipart (file upload) support ........................................................... 485

Introduction .................................................................................................... 485

Using a MultipartResolver with Commons FileUpload ........................................ 485

Using a MultipartResolver with Servlet 3.0 ....................................................... 486

Handling a file upload in a form ...................................................................... 486

Handling a file upload request from programmatic clients .................................. 487

17.11. Handling exceptions ..................................................................................... 488

HandlerExceptionResolver .............................................................................. 488

@ExceptionHandler ........................................................................................ 488

Handling Standard Spring MVC Exceptions ...................................................... 489

Annotating Business Exceptions With @ResponseStatus .................................. 490

Customizing the Default Servlet Container Error Page ...................................... 490

17.12. Web Security ............................................................................................... 491

17.13. Convention over configuration support ........................................................... 491

The Controller ControllerClassNameHandlerMapping ........................................ 491

The Model ModelMap (ModelAndView) ............................................................ 492

The View - RequestToViewNameTranslator ..................................................... 494

17.14. ETag support ............................................................................................... 495

17.15. Code-based Servlet container initialization ..................................................... 495

17.16. Configuring Spring MVC ............................................................................... 497

Enabling the MVC Java Config or the MVC XML Namespace ............................ 497

Customizing the Provided Configuration ........................................................... 499

Interceptors .................................................................................................... 499

Content Negotiation ........................................................................................ 500

View Controllers ............................................................................................. 501

View Resolvers .............................................................................................. 501

Serving of Resources ..................................................................................... 503

Falling Back On the "Default" Servlet To Serve Resources ................................ 505

Path Matching ................................................................................................ 506

Advanced Customizations with MVC Java Config ............................................. 506

Advanced Customizations with the MVC Namespace ........................................ 507

18. View technologies ..................................................................................................... 508

18.1. Introduction .................................................................................................... 508

18.2. JSP & JSTL .................................................................................................. 508

View resolvers ................................................................................................ 508

Plain-old JSPs versus JSTL ............................................................................ 509

Additional tags facilitating development ............................................................ 509

Using Spring’s form tag library ........................................................................ 509

Configuration .......................................................................................... 509

The form tag .......................................................................................... 509

The input tag .......................................................................................... 511

The checkbox tag ................................................................................... 511

The checkboxes tag ............................................................................... 513

The radiobutton tag ................................................................................ 513

The radiobuttons tag ............................................................................... 513

The password tag ................................................................................... 514

The select tag ........................................................................................ 514

The option tag ........................................................................................ 514

The options tag ...................................................................................... 515

The textarea tag ..................................................................................... 516

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xvii

The hidden tag ....................................................................................... 516

The errors tag ........................................................................................ 516

HTTP Method Conversion ....................................................................... 518

HTML5 Tags .......................................................................................... 519

18.3. Tiles .............................................................................................................. 519

Dependencies ................................................................................................ 519

How to integrate Tiles ..................................................................................... 519

UrlBasedViewResolver ............................................................................ 520

ResourceBundleViewResolver ................................................................. 520

SimpleSpringPreparerFactory and SpringBeanPreparerFactory ................. 521

18.4. Velocity & FreeMarker .................................................................................... 521

Dependencies ................................................................................................ 522

Context configuration ...................................................................................... 522

Creating templates ......................................................................................... 522

Advanced configuration ................................................................................... 523

velocity.properties ................................................................................... 523

FreeMarker ............................................................................................. 523

Bind support and form handling ....................................................................... 524

The bind macros .................................................................................... 524

Simple binding ........................................................................................ 524

Form input generation macros ................................................................. 525

HTML escaping and XHTML compliance ................................................. 528

18.5. XSLT ............................................................................................................. 529

My First Words ............................................................................................... 529

Bean definitions ...................................................................................... 529

Standard MVC controller code ................................................................. 529

Convert the model data to XML ............................................................... 530

Defining the view properties .................................................................... 530

Document transformation ........................................................................ 531

Summary ....................................................................................................... 531

18.6. Document views (PDF/Excel) .......................................................................... 532

Introduction .................................................................................................... 532

Configuration and setup .................................................................................. 532

Document view definitions ....................................................................... 532

Controller code ....................................................................................... 532

Subclassing for Excel views .................................................................... 532

Subclassing for PDF views ..................................................................... 534

18.7. JasperReports ............................................................................................... 534

Dependencies ................................................................................................ 534

Configuration .................................................................................................. 534

Configuring the ViewResolver .................................................................. 535

Configuring the Views ............................................................................. 535

About Report Files .................................................................................. 535

Using JasperReportsMultiFormatView ...................................................... 535

Populating the ModelAndView ......................................................................... 536

Working with Sub-Reports ............................................................................... 537

Configuring Sub-Report Files .................................................................. 537

Configuring Sub-Report Data Sources ..................................................... 538

Configuring Exporter Parameters ..................................................................... 538

18.8. Feed Views ................................................................................................... 539

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xviii

18.9. XML Marshalling View .................................................................................... 539

18.10. JSON Mapping View .................................................................................... 540

18.11. XML Mapping View ...................................................................................... 540

19. Integrating with other web frameworks ....................................................................... 541

19.1. Introduction .................................................................................................... 541

19.2. Common configuration ................................................................................... 542

19.3. JavaServer Faces 1.2 .................................................................................... 543

SpringBeanFacesELResolver (JSF 1.2+) ......................................................... 543

FacesContextUtils ........................................................................................... 543

19.4. Apache Struts 2.x .......................................................................................... 543

19.5. Tapestry 5.x .................................................................................................. 544

19.6. Further Resources ......................................................................................... 544

20. Portlet MVC Framework ............................................................................................ 545

20.1. Introduction .................................................................................................... 545

Controllers - The C in MVC ............................................................................ 546

Views - The V in MVC .................................................................................... 546

Web-scoped beans ......................................................................................... 546

20.2. The DispatcherPortlet ..................................................................................... 546

20.3. The ViewRendererServlet ............................................................................... 548

20.4. Controllers ..................................................................................................... 549

AbstractController and PortletContentGenerator ............................................... 550

Other simple controllers .................................................................................. 551

Command Controllers ..................................................................................... 551

PortletWrappingController ................................................................................ 552

20.5. Handler mappings .......................................................................................... 552

PortletModeHandlerMapping ............................................................................ 553

ParameterHandlerMapping .............................................................................. 553

PortletModeParameterHandlerMapping ............................................................ 554

Adding HandlerInterceptors ............................................................................. 554

HandlerInterceptorAdapter ............................................................................... 555

ParameterMappingInterceptor .......................................................................... 555

20.6. Views and resolving them .............................................................................. 555

20.7. Multipart (file upload) support ......................................................................... 555

Using the PortletMultipartResolver ................................................................... 556

Handling a file upload in a form ...................................................................... 556

20.8. Handling exceptions ....................................................................................... 560

20.9. Annotation-based controller configuration ........................................................ 560

Setting up the dispatcher for annotation support ............................................... 560

Defining a controller with @Controller .............................................................. 561

Mapping requests with @RequestMapping ....................................................... 561

Supported handler method arguments ............................................................. 563

Binding request parameters to method parameters with @RequestParam .......... 564

Providing a link to data from the model with @ModelAttribute ............................ 564

Specifying attributes to store in a Session with @SessionAttributes .................... 565

Customizing WebDataBinder initialization ......................................................... 565

Customizing data binding with @InitBinder ............................................... 566

Configuring a custom WebBindingInitializer .............................................. 566

20.10. Portlet application deployment ...................................................................... 566

21. WebSocket Support .................................................................................................. 568

21.1. Introduction .................................................................................................... 568

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xix

WebSocket Fallback Options ........................................................................... 568

A Messaging Architecture ............................................................................... 569

Sub-Protocol Support in WebSocket ................................................................ 569

Should I Use WebSocket? .............................................................................. 569

21.2. WebSocket API ............................................................................................. 570

Create and Configure a WebSocketHandler ..................................................... 570

Customizing the WebSocket Handshake .......................................................... 571

WebSocketHandler Decoration ........................................................................ 572

Deployment Considerations ............................................................................. 572

Configuring the WebSocket Engine ................................................................. 573

21.3. SockJS Fallback Options ................................................................................ 575

Overview of SockJS ....................................................................................... 575

Enable SockJS ............................................................................................... 576

HTTP Streaming in IE 8, 9: Ajax/XHR vs IFrame .............................................. 577

Heartbeat Messages ....................................................................................... 578

Servlet 3 Async Requests ............................................................................... 578

CORS Headers for SockJS ............................................................................. 579

SockJS Client ................................................................................................. 579

21.4. STOMP Over WebSocket Messaging Architecture ........................................... 580

Overview of STOMP ....................................................................................... 581

Enable STOMP over WebSocket ..................................................................... 582

Flow of Messages .......................................................................................... 583

Annotation Message Handling ......................................................................... 585

Sending Messages ......................................................................................... 586

Simple Broker ................................................................................................ 586

Full-Featured Broker ....................................................................................... 586

Connections To Full-Featured Broker .............................................................. 588

Using Dot as Separator in @MessageMapping Destinations ............................. 588

Authentication ................................................................................................. 589

User Destinations ........................................................................................... 590

Listening To ApplicationContext Events and Intercepting Messages ................... 591

WebSocket Scope .......................................................................................... 593

Configuration and Performance ....................................................................... 594

Runtime Monitoring ......................................................................................... 596

Testing Annotated Controller Methods ............................................................. 597

VI. Integration ......................................................................................................................... 599

22. Remoting and web services using Spring ................................................................... 600

22.1. Introduction .................................................................................................... 600

22.2. Exposing services using RMI .......................................................................... 601

Exporting the service using the RmiServiceExporter ......................................... 601

Linking in the service at the client ................................................................... 602

22.3. Using Hessian or Burlap to remotely call services via HTTP .............................. 602

Wiring up the DispatcherServlet for Hessian and co. ......................................... 602

Exposing your beans by using the HessianServiceExporter ............................... 603

Linking in the service on the client .................................................................. 603

Using Burlap .................................................................................................. 604

Applying HTTP basic authentication to a service exposed through Hessian or

Burlap ............................................................................................................ 604

22.4. Exposing services using HTTP invokers .......................................................... 604

Exposing the service object ............................................................................ 605

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xx

Linking in the service at the client ................................................................... 606

22.5. Web services ................................................................................................. 606

Exposing servlet-based web services using JAX-WS ........................................ 606

Exporting standalone web services using JAX-WS ........................................... 607

Exporting web services using the JAX-WS RI’s Spring support .......................... 608

Accessing web services using JAX-WS ........................................................... 608

22.6. JMS .............................................................................................................. 609

Server-side configuration ................................................................................. 610

Client-side configuration .................................................................................. 610

22.7. AMQP ........................................................................................................... 611

22.8. Auto-detection is not implemented for remote interfaces ................................... 611

22.9. Considerations when choosing a technology .................................................... 612

22.10. Accessing RESTful services on the Client ..................................................... 612

RestTemplate ................................................................................................. 612

Working with the URI .............................................................................. 615

Dealing with request and response headers ............................................. 616

Jackson JSON Views support ................................................................. 616

HTTP Message Conversion ............................................................................ 616

StringHttpMessageConverter ................................................................... 617

FormHttpMessageConverter .................................................................... 617

ByteArrayHttpMessageConverter ............................................................. 617

MarshallingHttpMessageConverter ........................................................... 617

MappingJackson2HttpMessageConverter ................................................. 617

MappingJackson2XmlHttpMessageConverter ........................................... 618

SourceHttpMessageConverter ................................................................. 618

BufferedImageHttpMessageConverter ...................................................... 618

Async RestTemplate ....................................................................................... 618

23. Enterprise JavaBeans (EJB) integration ..................................................................... 620

23.1. Introduction .................................................................................................... 620

23.2. Accessing EJBs ............................................................................................. 620

Concepts ........................................................................................................ 620

Accessing local SLSBs ................................................................................... 620

Accessing remote SLSBs ................................................................................ 622

Accessing EJB 2.x SLSBs versus EJB 3 SLSBs ............................................... 622

23.3. Using Spring’s EJB implementation support classes ......................................... 623

EJB 3 injection interceptor .............................................................................. 623

24. JMS (Java Message Service) .................................................................................... 624

24.1. Introduction .................................................................................................... 624

24.2. Using Spring JMS .......................................................................................... 624

JmsTemplate .................................................................................................. 624

Connections ................................................................................................... 625

Caching Messaging Resources ............................................................... 625

SingleConnectionFactory ......................................................................... 626

CachingConnectionFactory ...................................................................... 626

Destination Management ................................................................................. 626

Message Listener Containers .......................................................................... 627

SimpleMessageListenerContainer ............................................................ 627

DefaultMessageListenerContainer ............................................................ 627

Transaction management ................................................................................ 628

24.3. Sending a Message ....................................................................................... 628

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxi

Using Message Converters ............................................................................. 629

SessionCallback and ProducerCallback ........................................................... 630

24.4. Receiving a message ..................................................................................... 630

Synchronous Reception .................................................................................. 630

Asynchronous Reception - Message-Driven POJOs .......................................... 630

the SessionAwareMessageListener interface .................................................... 631

the MessageListenerAdapter ........................................................................... 632

Processing messages within transactions ........................................................ 634

24.5. Support for JCA Message Endpoints ............................................................... 634

24.6. Annotation-driven listener endpoints ................................................................ 636

Enable listener endpoint annotations ............................................................... 636

Programmatic endpoints registration ................................................................ 637

Annotated endpoint method signature .............................................................. 637

Reply management ......................................................................................... 638

24.7. JMS Namespace Support ............................................................................... 639

25. JMX ......................................................................................................................... 644

25.1. Introduction .................................................................................................... 644

25.2. Exporting your beans to JMX .......................................................................... 644

Creating an MBeanServer ............................................................................... 646

Reusing an existing MBeanServer ................................................................... 646

Lazy-initialized MBeans ................................................................................... 647

Automatic registration of MBeans .................................................................... 647

Controlling the registration behavior ................................................................. 647

25.3. Controlling the management interface of your beans ........................................ 648

the MBeanInfoAssembler Interface .................................................................. 649

Using Source-Level Metadata (Java annotations) ............................................. 649

Source-Level Metadata Types ......................................................................... 651

the AutodetectCapableMBeanInfoAssembler interface ...................................... 652

Defining management interfaces using Java interfaces ..................................... 653

Using MethodNameBasedMBeanInfoAssembler ............................................... 654

25.4. Controlling the ObjectNames for your beans .................................................... 655

Reading ObjectNames from Properties ............................................................ 655

Using the MetadataNamingStrategy ................................................................. 656

Configuring annotation based MBean export .................................................... 656

25.5. JSR-160 Connectors ...................................................................................... 657

Server-side Connectors ................................................................................... 657

Client-side Connectors .................................................................................... 658

JMX over Burlap/Hessian/SOAP ...................................................................... 658

25.6. Accessing MBeans via Proxies ....................................................................... 658

25.7. Notifications ................................................................................................... 659

Registering Listeners for Notifications .............................................................. 659

Publishing Notifications ................................................................................... 662

25.8. Further Resources ......................................................................................... 663

26. JCA CCI .................................................................................................................. 665

26.1. Introduction .................................................................................................... 665

26.2. Configuring CCI ............................................................................................. 665

Connector configuration .................................................................................. 665

ConnectionFactory configuration in Spring ....................................................... 666

Configuring CCI connections ........................................................................... 666

Using a single CCI connection ........................................................................ 667

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxii

26.3. Using Spring’s CCI access support ................................................................. 668

Record conversion .......................................................................................... 668

the CciTemplate ............................................................................................. 668

DAO support .................................................................................................. 670

Automatic output record generation ................................................................. 671

Summary ....................................................................................................... 671

Using a CCI Connection and Interaction directly ............................................... 672

Example for CciTemplate usage ...................................................................... 672

26.4. Modeling CCI access as operation objects ...................................................... 674

MappingRecordOperation ................................................................................ 674

MappingCommAreaOperation .......................................................................... 675

Automatic output record generation ................................................................. 676

Summary ....................................................................................................... 676

Example for MappingRecordOperation usage ................................................... 676

Example for MappingCommAreaOperation usage ............................................. 678

26.5. Transactions .................................................................................................. 680

27. Email ....................................................................................................................... 681

27.1. Introduction .................................................................................................... 681

27.2. Usage ........................................................................................................... 681

Basic MailSender and SimpleMailMessage usage ............................................ 682

Using the JavaMailSender and the MimeMessagePreparator ............................. 682

27.3. Using the JavaMail MimeMessageHelper ........................................................ 683

Sending attachments and inline resources ....................................................... 684

Attachments ........................................................................................... 684

Inline resources ...................................................................................... 684

Creating email content using a templating library .............................................. 685

A Velocity-based example ....................................................................... 685

28. Task Execution and Scheduling ................................................................................. 688

28.1. Introduction .................................................................................................... 688

28.2. The Spring TaskExecutor abstraction .............................................................. 688

TaskExecutor types ........................................................................................ 688

Using a TaskExecutor ..................................................................................... 689

28.3. The Spring TaskScheduler abstraction ............................................................ 690

the Trigger interface ....................................................................................... 691

Trigger implementations .................................................................................. 691

TaskScheduler implementations ...................................................................... 692

28.4. Annotation Support for Scheduling and Asynchronous Execution ....................... 692

Enable scheduling annotations ........................................................................ 692

The @Scheduled Annotation ........................................................................... 693

The @Async Annotation ................................................................................. 694

Executor qualification with @Async ................................................................. 695

Exception management with @Async .............................................................. 695

28.5. The Task Namespace .................................................................................... 695

The scheduler element ................................................................................... 695

The executor element ..................................................................................... 695

The scheduled-tasks element .......................................................................... 697

28.6. Using the Quartz Scheduler ............................................................................ 697

Using the JobDetailBean ................................................................................. 697

Using the MethodInvokingJobDetailFactoryBean .............................................. 698

Wiring up jobs using triggers and the SchedulerFactoryBean ............................. 699

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxiii

29. Dynamic language support ........................................................................................ 700

29.1. Introduction .................................................................................................... 700

29.2. A first example .............................................................................................. 700

29.3. Defining beans that are backed by dynamic languages ..................................... 702

Common concepts .......................................................................................... 702

The <lang:language/> element ................................................................ 703

Refreshable beans .................................................................................. 703

Inline dynamic language source files ....................................................... 705

Understanding Constructor Injection in the context of dynamic-language-

backed beans ......................................................................................... 706

JRuby beans .................................................................................................. 707

Groovy beans ................................................................................................. 708

Customizing Groovy objects via a callback ............................................... 709

BeanShell beans ............................................................................................ 711

29.4. Scenarios ...................................................................................................... 712

Scripted Spring MVC Controllers ..................................................................... 712

Scripted Validators ......................................................................................... 713

29.5. Bits and bobs ................................................................................................ 713

AOP - advising scripted beans ........................................................................ 713

Scoping .......................................................................................................... 714

29.6. Further Resources ......................................................................................... 714

30. Cache Abstraction .................................................................................................... 715

30.1. Introduction .................................................................................................... 715

30.2. Understanding the cache abstraction ............................................................... 715

30.3. Declarative annotation-based caching ............................................................. 716

@Cacheable annotation .................................................................................. 716

Default Key Generation ........................................................................... 717

Custom Key Generation Declaration ........................................................ 717

Default Cache Resolution ........................................................................ 718

Custom cache resolution ......................................................................... 718

Conditional caching ................................................................................ 719

Available caching SpEL evaluation context ............................................... 719

@CachePut annotation ................................................................................... 720

@CacheEvict annotation ................................................................................. 721

@Caching annotation ..................................................................................... 721

@CacheConfig annotation .............................................................................. 721

Enable caching annotations ............................................................................ 722

Using custom annotations ............................................................................... 725

30.4. JCache (JSR-107) annotations ....................................................................... 725

Features summary .......................................................................................... 725

Enabling JSR-107 support .............................................................................. 727

30.5. Declarative XML-based caching ...................................................................... 727

30.6. Configuring the cache storage ........................................................................ 728

JDK ConcurrentMap-based Cache ................................................................... 728

EhCache-based Cache ................................................................................... 728

Guava Cache ................................................................................................. 729

GemFire-based Cache .................................................................................... 729

JSR-107 Cache .............................................................................................. 729

Dealing with caches without a backing store .................................................... 729

30.7. Plugging-in different back-end caches ............................................................. 730

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxiv

30.8. How can I set the TTL/TTI/Eviction policy/XXX feature? .................................... 730

VII. Appendices ...................................................................................................................... 731

31. Migrating to Spring Framework 4.0 ............................................................................ 732

32. Classic Spring Usage ............................................................................................... 733

32.1. Classic ORM usage ....................................................................................... 733

Hibernate ....................................................................................................... 733

the HibernateTemplate ............................................................................ 733

Implementing Spring-based DAOs without callbacks ................................. 734

JDO ............................................................................................................... 735

JdoTemplate and JdoDaoSupport ......................................................... 735

JPA ................................................................................................................ 736

JpaTemplate and JpaDaoSupport ......................................................... 736

32.2. Classic Spring MVC ....................................................................................... 738

32.3. JMS Usage ................................................................................................... 738

JmsTemplate .................................................................................................. 738

Asynchronous Message Reception .................................................................. 738

Connections ................................................................................................... 739

Transaction Management ................................................................................ 739

33. Classic Spring AOP Usage ....................................................................................... 740

33.1. Pointcut API in Spring .................................................................................... 740

Concepts ........................................................................................................ 740

Operations on pointcuts .................................................................................. 741

AspectJ expression pointcuts .......................................................................... 741

Convenience pointcut implementations ............................................................ 741

Static pointcuts ....................................................................................... 741

Dynamic pointcuts .................................................................................. 742

Pointcut superclasses ..................................................................................... 743

Custom pointcuts ............................................................................................ 743

33.2. Advice API in Spring ...................................................................................... 743

Advice lifecycles ............................................................................................. 743

Advice types in Spring .................................................................................... 744

Interception around advice ...................................................................... 744

Before advice ......................................................................................... 744

Throws advice ........................................................................................ 745

After Returning advice ............................................................................ 746

Introduction advice .................................................................................. 747

33.3. Advisor API in Spring ..................................................................................... 749

33.4. Using the ProxyFactoryBean to create AOP proxies ......................................... 750

Basics ............................................................................................................ 750

JavaBean properties ....................................................................................... 750

JDK- and CGLIB-based proxies ...................................................................... 751

Proxying interfaces ......................................................................................... 752

Proxying classes ............................................................................................ 754

Using global advisors ...................................................................................... 755

33.5. Concise proxy definitions ................................................................................ 755

33.6. Creating AOP proxies programmatically with the ProxyFactory .......................... 756

33.7. Manipulating advised objects .......................................................................... 756

33.8. Using the "autoproxy" facility .......................................................................... 758

Autoproxy bean definitions .............................................................................. 758

BeanNameAutoProxyCreator ................................................................... 758

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxv

DefaultAdvisorAutoProxyCreator .............................................................. 759

AbstractAdvisorAutoProxyCreator ............................................................ 760

Using metadata-driven auto-proxying ............................................................... 760

33.9. Using TargetSources ...................................................................................... 762

Hot swappable target sources ......................................................................... 762

Pooling target sources .................................................................................... 763

Prototype target sources ................................................................................. 764

ThreadLocal target sources ............................................................................. 764

33.10. Defining new Advice types ............................................................................ 764

33.11. Further resources ......................................................................................... 765

34. XML Schema-based configuration ............................................................................. 766

34.1. Introduction .................................................................................................... 766

34.2. XML Schema-based configuration ................................................................... 766

Referencing the schemas ............................................................................... 766

the util schema ............................................................................................... 767

<util:constant/> ....................................................................................... 768

<util:property-path/> ................................................................................ 769

<util:properties/> ..................................................................................... 771

<util:list/> ................................................................................................ 771

<util:map/> ............................................................................................. 772

<util:set/> ............................................................................................... 772

the jee schema .............................................................................................. 773

<jee:jndi-lookup/> (simple) ....................................................................... 773

<jee:jndi-lookup/> (with single JNDI environment setting) .......................... 774

<jee:jndi-lookup/> (with multiple JNDI environment settings) ...................... 774

<jee:jndi-lookup/> (complex) .................................................................... 774

<jee:local-slsb/> (simple) ......................................................................... 775

<jee:local-slsb/> (complex) ...................................................................... 775

<jee:remote-slsb/> .................................................................................. 775

the lang schema ............................................................................................. 776

the jms schema .............................................................................................. 776

the tx (transaction) schema ............................................................................. 777

the aop schema ............................................................................................. 777

the context schema ........................................................................................ 778

<property-placeholder/> ........................................................................... 778

<annotation-config/> ............................................................................... 778

<component-scan/> ................................................................................ 778

<load-time-weaver/> ............................................................................... 779

<spring-configured/> ............................................................................... 779

<mbean-export/> .................................................................................... 779

the tool schema .............................................................................................. 779

the jdbc schema ............................................................................................. 779

the cache schema .......................................................................................... 779

the beans schema .......................................................................................... 780

35. Extensible XML authoring ......................................................................................... 781

35.1. Introduction .................................................................................................... 781

35.2. Authoring the schema .................................................................................... 781

35.3. Coding a NamespaceHandler ......................................................................... 782

35.4. BeanDefinitionParser ...................................................................................... 783

35.5. Registering the handler and the schema ......................................................... 784

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework xxvi

META-INF/spring.handlers .............................................................................. 784

META-INF/spring.schemas .............................................................................. 785

35.6. Using a custom extension in your Spring XML configuration .............................. 785

35.7. Meatier examples ........................................................................................... 785

Nesting custom tags within custom tags .......................................................... 785

Custom attributes on normal elements ............................................................. 789

35.8. Further Resources ......................................................................................... 791

36. spring.tld .................................................................................................................. 792

36.1. Introduction .................................................................................................... 792

36.2. the bind tag ................................................................................................... 792

36.3. the escapeBody tag ....................................................................................... 793

36.4. the hasBindErrors tag .................................................................................... 793

36.5. the htmlEscape tag ........................................................................................ 793

36.6. the message tag ............................................................................................ 793

36.7. the nestedPath tag ......................................................................................... 794

36.8. the theme tag ................................................................................................ 795

36.9. the transform tag ........................................................................................... 796

36.10. the url tag .................................................................................................... 796

36.11. the eval tag ................................................................................................. 797

37. spring-form.tld ........................................................................................................... 798

37.1. Introduction .................................................................................................... 798

37.2. the checkbox tag ........................................................................................... 798

37.3. the checkboxes tag ........................................................................................ 799

37.4. the errors tag ................................................................................................. 801

37.5. the form tag ................................................................................................... 802

37.6. the hidden tag ............................................................................................... 803

37.7. the input tag .................................................................................................. 803

37.8. the label tag .................................................................................................. 805

37.9. the option tag ................................................................................................ 806

37.10. the options tag ............................................................................................. 807

37.11. the password tag ......................................................................................... 808

37.12. the radiobutton tag ....................................................................................... 809

37.13. the radiobuttons tag ..................................................................................... 810

37.14. the select tag ............................................................................................... 812

37.15. the textarea tag ........................................................................................... 813

Part I. Overview of Spring Framework

The Spring Framework is a lightweight solution and a potential one-stop-shop for building your

enterprise-ready applications. However, Spring is modular, allowing you to use only those parts that you

need, without having to bring in the rest. You can use the IoC container, with any web framework on

top, but you can also use only the Hibernate integration code or the JDBC abstraction layer. The Spring

Framework supports declarative transaction management, remote access to your logic through RMI or

web services, and various options for persisting your data. It offers a full-featured MVC framework, and

enables you to integrate AOP transparently into your software.

Spring is designed to be non-intrusive, meaning that your domain logic code generally has no

dependencies on the framework itself. In your integration layer (such as the data access layer), some

dependencies on the data access technology and the Spring libraries will exist. However, it should be

easy to isolate these dependencies from the rest of your code base.

This document is a reference guide to Spring Framework features. If you have any requests, comments,

or questions on this document, please post them on the user mailing list. Questions on the Framework

itself should be asked on StackOverflow (see https://spring.io/questions).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 2

1. Getting Started With Spring

This reference guide provides detailed information about the Spring Framework. It provides

comprehensive documentation for all features, as well as some background about the underlying

concepts (such as "Dependency Injection") that Spring has embraced.

If you are just getting started with Spring, you may want to begin with the lighter "Getting Started" guides

that are available from https://spring.io. As well as being easier to digest, these guide are very task

focused. They also cover other projects from the Spring portfolio that you might want to consider when

solving a particular problem.

Getting Started Building a RESTful Web Service would be an excellent first choice to get your feet wet.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 3

2. Introduction to Spring Framework

Spring Framework is a Java platform that provides comprehensive infrastructure support for developing

Java applications. Spring handles the infrastructure so you can focus on your application.

Spring enables you to build applications from "plain old Java objects" (POJOs) and to apply enterprise

services non-invasively to POJOs. This capability applies to the Java SE programming model and to

full and partial Java EE.

Examples of how you, as an application developer, can use the Spring platform advantage:

• Make a Java method execute in a database transaction without having to deal with transaction APIs.

• Make a local Java method a remote procedure without having to deal with remote APIs.

• Make a local Java method a management operation without having to deal with JMX APIs.

• Make a local Java method a message handler without having to deal with JMS APIs.

2.1 Dependency Injection and Inversion of Control

Background

"The question is, what aspect of control are [they] inverting?" Martin Fowler posed this question

about Inversion of Control (IoC) on his site in 2004. Fowler suggested renaming the principle to

make it more self-explanatory and came up with Dependency Injection.

For insight into IoC and DI, refer to Fowler’s article at http://martinfowler.com/articles/injection.html.

Java applications — a loose term that runs the gamut from constrained applets to n-tier server-side

enterprise applications — typically consist of objects that collaborate to form the application proper. Thus

the objects in an application have dependencies on each other.

Although the Java platform provides a wealth of application development functionality, it lacks the

means to organize the basic building blocks into a coherent whole, leaving that task to architects and

developers. True, you can use design patterns such as Factory, Abstract Factory, Builder, Decorator,

and Service Locator to compose the various classes and object instances that make up an application.

However, these patterns are simply that: best practices given a name, with a description of what the

pattern does, where to apply it, the problems it addresses, and so forth. Patterns are formalized best

practices that you must implement yourself in your application.

The Spring Framework Inversion of Control (IoC) component addresses this concern by providing a

formalized means of composing disparate components into a fully working application ready for use.

The Spring Framework codifies formalized design patterns as first-class objects that you can integrate

into your own application(s). Numerous organizations and institutions use the Spring Framework in this

manner to engineer robust, maintainable applications.

2.2 Modules

The Spring Framework consists of features organized into about 20 modules. These modules are

grouped into Core Container, Data Access/Integration, Web, AOP (Aspect Oriented Programming),

Instrumentation, Messaging, and Test, as shown in the following diagram.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 4

Figure 2.1. Overview of the Spring Framework

The following sections list the available modules for each feature along with their artifact name and the

topics they cover. Artifact names correlate to artifact IDs used in Dependency Management tools.

Core Container

The Core Container consists of the spring-core, spring-beans, spring-context, and spring-

expression (Spring Expression Language) modules.

The spring-core and spring-beans modules provide the fundamental parts of the framework,

including the IoC and Dependency Injection features. The BeanFactory is a sophisticated

implementation of the factory pattern. It removes the need for programmatic singletons and allows you

to decouple the configuration and specification of dependencies from your actual program logic.

The Context (spring-context) module builds on the solid base provided by the Core and Beans

modules: it is a means to access objects in a framework-style manner that is similar to a JNDI registry.

The Context module inherits its features from the Beans module and adds support for internationalization

(using, for example, resource bundles), event propagation, resource loading, and the transparent

creation of contexts by, for example, a Servlet container. The Context module also supports Java EE

features such as EJB, JMX, and basic remoting. The ApplicationContext interface is the focal point

of the Context module.

The spring-expression module provides a powerful Expression Language for querying and

manipulating an object graph at runtime. It is an extension of the unified expression language (unified

EL) as specified in the JSP 2.1 specification. The language supports setting and getting property values,

property assignment, method invocation, accessing the content of arrays, collections and indexers,

logical and arithmetic operators, named variables, and retrieval of objects by name from Spring’s IoC

container. It also supports list projection and selection as well as common list aggregations.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 5

AOP and Instrumentation

The spring-aop module provides an AOP Alliance-compliant aspect-oriented programming

implementation allowing you to define, for example, method interceptors and pointcuts to cleanly

decouple code that implements functionality that should be separated. Using source-level metadata

functionality, you can also incorporate behavioral information into your code, in a manner similar to that

of .NET attributes.

The separate spring-aspects module provides integration with AspectJ.

The spring-instrument module provides class instrumentation support and classloader

implementations to be used in certain application servers.

Messaging

Spring Framework 4 includes a spring-messaging module with key abstractions from the Spring

Integration project such as Message, MessageChannel, MessageHandler, and others to serve as a

foundation for messaging-based applications. The module also includes a set of annotations for mapping

messages to methods, similar to the Spring MVC annotation based programming model.

Data Access/Integration

The Data Access/Integration layer consists of the JDBC, ORM, OXM, JMS, and Transaction modules.

The spring-jdbc module provides a JDBC-abstraction layer that removes the need to do tedious

JDBC coding and parsing of database-vendor specific error codes.

The spring-orm module provides integration layers for popular object-relational mapping APIs,

including JPA, JDO, and Hibernate. Using the spring-orm module you can use all of these O/R-

mapping frameworks in combination with all of the other features Spring offers, such as the simple

declarative transaction management feature mentioned previously.

The spring-oxm module provides an abstraction layer that supports Object/XML mapping

implementations such as JAXB, Castor, XMLBeans, JiBX and XStream.

The spring-jms module (Java Messaging Service) contains features for producing and consuming

messages. Since Spring Framework 4.1, it provides integration with the spring-messaging module.

The spring-tx module supports programmatic and declarative transaction management for classes

that implement special interfaces and for all your POJOs (Plain Old Java Objects).

Web

The Web layer consists of the spring-web, spring-webmvc, spring-websocket, and spring-

webmvc-portlet modules.

The spring-web module provides basic web-oriented integration features such as multipart file upload

functionality and the initialization of the IoC container using Servlet listeners and a web-oriented

application context. It also contains the web-related parts of Spring’s remoting support.

The spring-webmvc module (also known as the Web-Servlet module) contains Spring’s model-

view-controller (MVC) implementation for web applications. Spring’s MVC framework provides a clean

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 6

separation between domain model code and web forms and integrates with all of the other features of

the Spring Framework.

The spring-webmvc-portlet module (also known as the Web-Portlet module) provides the MVC

implementation to be used in a Portlet environment and mirrors the functionality of the spring-webmvc

module.

Test

The spring-test module supports the unit testing and integration testing of Spring components with

JUnit or TestNG. It provides consistent loading of Spring ApplicationContexts and caching of those

contexts. It also provides mock objects that you can use to test your code in isolation.

2.3 Usage scenarios

The building blocks described previously make Spring a logical choice in many scenarios, from applets

to full-fledged enterprise applications that use Spring’s transaction management functionality and web

framework integration.

Figure 2.2. Typical full-fledged Spring web application

Spring’s declarative transaction management features make the web application fully transactional, just

as it would be if you used EJB container-managed transactions. All your custom business logic can be

implemented with simple POJOs and managed by Spring’s IoC container. Additional services include

support for sending email and validation that is independent of the web layer, which lets you choose

where to execute validation rules. Spring’s ORM support is integrated with JPA, Hibernate and and

JDO; for example, when using Hibernate, you can continue to use your existing mapping files and

standard Hibernate SessionFactory configuration. Form controllers seamlessly integrate the web-

layer with the domain model, removing the need for ActionForms or other classes that transform HTTP

parameters to values for your domain model.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 7

Figure 2.3. Spring middle-tier using a third-party web framework

Sometimes circumstances do not allow you to completely switch to a different framework. The Spring

Framework does not force you to use everything within it; it is not an all-or-nothing solution. Existing

front-ends built with Struts, Tapestry, JSF or other UI frameworks can be integrated with a Spring-

based middle-tier, which allows you to use Spring transaction features. You simply need to wire up your

business logic using an ApplicationContext and use a WebApplicationContext to integrate

your web layer.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 8

Figure 2.4. Remoting usage scenario

When you need to access existing code through web services, you can use Spring’s Hessian-,

Burlap-, Rmi- or JaxRpcProxyFactory classes. Enabling remote access to existing applications

is not difficult.

Figure 2.5. EJBs - Wrapping existing POJOs

The Spring Framework also provides an access and abstraction layer for Enterprise JavaBeans,

enabling you to reuse your existing POJOs and wrap them in stateless session beans for use in scalable,

fail-safe web applications that might need declarative security.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 9

Dependency Management and Naming Conventions

Dependency management and dependency injection are different things. To get those nice features of

Spring into your application (like dependency injection) you need to assemble all the libraries needed (jar

files) and get them onto your classpath at runtime, and possibly at compile time. These dependencies

are not virtual components that are injected, but physical resources in a file system (typically). The

process of dependency management involves locating those resources, storing them and adding them

to classpaths. Dependencies can be direct (e.g. my application depends on Spring at runtime), or indirect

(e.g. my application depends on commons-dbcp which depends on commons-pool). The indirect

dependencies are also known as "transitive" and it is those dependencies that are hardest to identify

and manage.

If you are going to use Spring you need to get a copy of the jar libraries that comprise the pieces of

Spring that you need. To make this easier Spring is packaged as a set of modules that separate the

dependencies as much as possible, so for example if you don’t want to write a web application you

don’t need the spring-web modules. To refer to Spring library modules in this guide we use a shorthand

naming convention spring-* or spring-*.jar, where * represents the short name for the module

(e.g. spring-core, spring-webmvc, spring-jms, etc.). The actual jar file name that you use is

normally the module name concatenated with the version number (e.g. spring-core-4.1.0.RELEASE.jar).

Each release of the Spring Framework will publish artifacts to the following places:

• Maven Central, which is the default repository that Maven queries, and does not require any special

configuration to use. Many of the common libraries that Spring depends on also are available

from Maven Central and a large section of the Spring community uses Maven for dependency

management, so this is convenient for them. The names of the jars here are in the form spring-*-

<version>.jar and the Maven groupId is org.springframework.

• In a public Maven repository hosted specifically for Spring. In addition to the final GA releases, this

repository also hosts development snapshots and milestones. The jar file names are in the same form

as Maven Central, so this is a useful place to get development versions of Spring to use with other

libraries deployed in Maven Central. This repository also contains a bundle distribution zip file that

contains all Spring jars bundled together for easy download.

So the first thing you need to decide is how to manage your dependencies: we generally recommend the

use of an automated system like Maven, Gradle or Ivy, but you can also do it manually by downloading

all the jars yourself. We provide detailed instructions later in this chapter.

Spring Dependencies and Depending on Spring

Although Spring provides integration and support for a huge range of enterprise and other external tools,

it intentionally keeps its mandatory dependencies to an absolute minimum: you shouldn’t have to locate

and download (even automatically) a large number of jar libraries in order to use Spring for simple use

cases. For basic dependency injection there is only one mandatory external dependency, and that is

for logging (see below for a more detailed description of logging options).

Next we outline the basic steps needed to configure an application that depends on Spring, first with

Maven and then with Gradle and finally using Ivy. In all cases, if anything is unclear, refer to the

documentation of your dependency management system, or look at some sample code - Spring itself

uses Gradle to manage dependencies when it is building, and our samples mostly use Gradle or Maven.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 10

Maven Dependency Management

If you are using Maven for dependency management you don’t even need to supply the logging

dependency explicitly. For example, to create an application context and use dependency injection to

configure an application, your Maven dependencies will look like this:

<groupId>org.springframework</groupId>

<artifactId>spring-context</artifactId>

<version>4.1.0.RELEASE</version>

<scope>runtime</scope>

</dependency>

</dependencies>

That’s it. Note the scope can be declared as runtime if you don’t need to compile against Spring APIs,

which is typically the case for basic dependency injection use cases.

The example above works with the Maven Central repository. To use the Spring Maven repository

(e.g. for milestones or developer snapshots), you need to specify the repository location in your Maven

configuration. For full releases:

<id>io.spring.repo.maven.release</id>

<url>http://repo.spring.io/release/</url>

<snapshots><enabled>false</enabled></snapshots>

</repository>

</repositories>

For milestones:

<id>io.spring.repo.maven.milestone</id>

<url>http://repo.spring.io/milestone/</url>

<snapshots><enabled>false</enabled></snapshots>

</repository>

</repositories>

And for snapshots:

<id>io.spring.repo.maven.snapshot</id>

<url>http://repo.spring.io/snapshot/</url>

</repository>

</repositories>

Maven "Bill Of Materials" Dependency

It is possible to accidentally mix different versions of Spring JARs when using Maven. For example,

you may find that a third-party library, or another Spring project, pulls in a transitive dependency to an

older release. If you forget to explicitly declare a direct dependency yourself, all sorts of unexpected

issues can arise.

To overcome such problems Maven supports the concept of a "bill of materials" (BOM) dependency.

You can import the spring-framework-bom in your dependencyManagement section to ensure

that all spring dependencies (both direct and transitive) are at the same version.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 11

<groupId>org.springframework</groupId>

<artifactId>spring-framework-bom</artifactId>

<version>4.1.0.RELEASE</version>

<scope>import</scope>

</dependency>

</dependencies>

</dependencyManagement>

An added benefit of using the BOM is that you no longer need to specify the <version> attribute when

depending on Spring Framework artifacts:

<groupId>org.springframework</groupId>

<artifactId>spring-context</artifactId>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-web</artifactId>

</dependency>

Gradle Dependency Management

To use the Spring repository with the Gradle build system, include the appropriate URL in the

repositories section:

repositories {

mavenCentral()

// and optionally...

maven { url "http://repo.spring.io/release" }

}

You can change the repositories URL from /release to /milestone or /snapshot as

appropriate. Once a repository has been configured, you can declare dependencies in the usual Gradle

way:

dependencies {

compile("org.springframework:spring-context:4.1.0.RELEASE")

testCompile("org.springframework:spring-test:4.1.0.RELEASE")

}

Ivy Dependency Management

If you prefer to use Ivy to manage dependencies then there are similar configuration options.

To configure Ivy to point to the Spring repository add the following resolver to your ivysettings.xml:

<ibiblio name="io.spring.repo.maven.release"

m2compatible="true"

root="http://repo.spring.io/release/"/>

</resolvers>

You can change the root URL from /release/ to /milestone/ or /snapshot/ as appropriate.

Once configured, you can add dependencies in the usual way. For example (in ivy.xml):

<dependency org="org.springframework"

name="spring-core" rev="4.1.0.RELEASE" conf="compile->runtime"/>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 12

Distribution Zip Files

Although using a build system that supports dependency management is the recommended way to

obtain the Spring Framework, it is still possible to download a distribution zip file.

Distribution zips are published to the Spring Maven Repository (this is just for our convenience, you

don’t need Maven or any other build system in order to download them).

To download a distribution zip open a web browser to http://repo.spring.io/release/org/springframework/

spring and select the appropriate subfolder for the version that you want. Distribution files end -

dist.zip, for example spring-framework-4.1.0.RELEASE-RELEASE-dist.zip. Distributions

are also published for milestones and snapshots.

Logging

Logging is a very important dependency for Spring because a) it is the only mandatory external

dependency, b) everyone likes to see some output from the tools they are using, and c) Spring integrates

with lots of other tools all of which have also made a choice of logging dependency. One of the goals

of an application developer is often to have unified logging configured in a central place for the whole

application, including all external components. This is more difficult than it might have been since there

are so many choices of logging framework.

The mandatory logging dependency in Spring is the Jakarta Commons Logging API (JCL). We compile

against JCL and we also make JCL Log objects visible for classes that extend the Spring Framework.

It’s important to users that all versions of Spring use the same logging library: migration is easy because

backwards compatibility is preserved even with applications that extend Spring. The way we do this

is to make one of the modules in Spring depend explicitly on commons-logging (the canonical

implementation of JCL), and then make all the other modules depend on that at compile time. If you are

using Maven for example, and wondering where you picked up the dependency on commons-logging,

then it is from Spring and specifically from the central module called spring-core.

The nice thing about commons-logging is that you don’t need anything else to make your application

work. It has a runtime discovery algorithm that looks for other logging frameworks in well known places

on the classpath and uses one that it thinks is appropriate (or you can tell it which one if you need to).

If nothing else is available you get pretty nice looking logs just from the JDK (java.util.logging or JUL

for short). You should find that your Spring application works and logs happily to the console out of the

box in most situations, and that’s important.

Not Using Commons Logging

Unfortunately, the runtime discovery algorithm in commons-logging, while convenient for the end-

user, is problematic. If we could turn back the clock and start Spring now as a new project it would use

a different logging dependency. The first choice would probably be the Simple Logging Facade for Java

( SLF4J), which is also used by a lot of other tools that people use with Spring inside their applications.

There are basically two ways to switch off commons-logging:

1. Exclude the dependency from the spring-core module (as it is the only module that explicitly

depends on commons-logging)

2. Depend on a special commons-logging dependency that replaces the library with an empty jar

(more details can be found in the SLF4J FAQ)

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 13

To exclude commons-logging, add the following to your dependencyManagement section:

<groupId>org.springframework</groupId>

<artifactId>spring-core</artifactId>

<version>4.1.0.RELEASE</version>

<groupId>commons-logging</groupId>

<artifactId>commons-logging</artifactId>

</exclusion>

</exclusions>

</dependency>

</dependencies>

Now this application is probably broken because there is no implementation of the JCL API on the

classpath, so to fix it a new one has to be provided. In the next section we show you how to provide an

alternative implementation of JCL using SLF4J as an example.

Using SLF4J

SLF4J is a cleaner dependency and more efficient at runtime than commons-logging because it uses

compile-time bindings instead of runtime discovery of the other logging frameworks it integrates. This

also means that you have to be more explicit about what you want to happen at runtime, and declare it

or configure it accordingly. SLF4J provides bindings to many common logging frameworks, so you can

usually choose one that you already use, and bind to that for configuration and management.

SLF4J provides bindings to many common logging frameworks, including JCL, and it also does the

reverse: bridges between other logging frameworks and itself. So to use SLF4J with Spring you need

to replace the commons-logging dependency with the SLF4J-JCL bridge. Once you have done that

then logging calls from within Spring will be translated into logging calls to the SLF4J API, so if other

libraries in your application use that API, then you have a single place to configure and manage logging.

A common choice might be to bridge Spring to SLF4J, and then provide explicit binding from SLF4J to

Log4J. You need to supply 4 dependencies (and exclude the existing commons-logging): the bridge,

the SLF4J API, the binding to Log4J, and the Log4J implementation itself. In Maven you would do that

like this

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 14

<groupId>org.springframework</groupId>

<artifactId>spring-core</artifactId>

<version>4.1.0.RELEASE</version>

<groupId>commons-logging</groupId>

<artifactId>commons-logging</artifactId>

</exclusion>

</exclusions>

</dependency>

</dependency>

</dependency>

</dependency>

</dependency>

</dependencies>

That might seem like a lot of dependencies just to get some logging. Well it is, but it is optional, and it

should behave better than the vanilla commons-logging with respect to classloader issues, notably if

you are in a strict container like an OSGi platform. Allegedly there is also a performance benefit because

the bindings are at compile-time not runtime.

A more common choice amongst SLF4J users, which uses fewer steps and generates fewer

dependencies, is to bind directly to Logback. This removes the extra binding step because Logback

implements SLF4J directly, so you only need to depend on two libraries not four ( jcl-over-slf4j and

logback). If you do that you might also need to exclude the slf4j-api dependency from other external

dependencies (not Spring), because you only want one version of that API on the classpath.

Using Log4J

Many people use Log4j as a logging framework for configuration and management purposes. It’s efficient

and well-established, and in fact it’s what we use at runtime when we build and test Spring. Spring

also provides some utilities for configuring and initializing Log4j, so it has an optional compile-time

dependency on Log4j in some modules.

To make Log4j work with the default JCL dependency ( commons-logging) all you need to do is put

Log4j on the classpath, and provide it with a configuration file ( log4j.properties or log4j.xml in

the root of the classpath). So for Maven users this is your dependency declaration:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 15

<groupId>org.springframework</groupId>

<artifactId>spring-core</artifactId>

<version>4.1.0.RELEASE</version>

</dependency>

</dependency>

</dependencies>

And here’s a sample log4j.properties for logging to the console:

log4j.rootCategory=INFO, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.stdout.layout=org.apache.log4j.PatternLayout

log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c{2}:%L - %m%n

log4j.category.org.springframework.beans.factory=DEBUG

Runtime Containers with Native JCL

Many people run their Spring applications in a container that itself provides an implementation

of JCL. IBM Websphere Application Server (WAS) is the archetype. This often causes problems,

and unfortunately there is no silver bullet solution; simply excluding commons-logging from your

application is not enough in most situations.

To be clear about this: the problems reported are usually not with JCL per se, or even with commons-

logging: rather they are to do with binding commons-logging to another framework (often Log4J).

This can fail because commons-logging changed the way they do the runtime discovery in between

the older versions (1.0) found in some containers and the modern versions that most people use now

(1.1). Spring does not use any unusual parts of the JCL API, so nothing breaks there, but as soon as

Spring or your application tries to do any logging you can find that the bindings to Log4J are not working.

In such cases with WAS the easiest thing to do is to invert the class loader hierarchy (IBM calls it "parent

last") so that the application controls the JCL dependency, not the container. That option isn’t always

open, but there are plenty of other suggestions in the public domain for alternative approaches, and

your mileage may vary depending on the exact version and feature set of the container.

Part II. What’s New in

Spring Framework 4.x

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 17

3. New Features and Enhancements in Spring

Framework 4.0

The Spring Framework was first released in 2004; since then there have been significant major revisions:

Spring 2.0 provided XML namespaces and AspectJ support; Spring 2.5 embraced annotation-driven

configuration; Spring 3.0 introduced a strong Java 5+ foundation across the framework codebase, and

features such as the Java-based @Configuration model.

Version 4.0 is the latest major release of the Spring Framework and the first to fully support Java 8

features. You can still use Spring with older versions of Java, however, the minimum requirement has

now been raised to Java SE 6. We have also taken the opportunity of a major release to remove many

deprecated classes and methods.

A migration guide for upgrading to Spring 4.0 is available on the Spring Framework GitHub Wiki.

3.1 Improved Getting Started Experience

The new spring.io website provides a whole series of "Getting Started" guides to help you learn Spring.

You can read more about the guides in the Chapter 1, Getting Started With Spring section in this

document. The new website also provides a comprehensive overview of the many additional projects

that are released under the Spring umbrella.

If you are a Maven user you may also be interested in the helpful bill of materials POM file that is now

published with each Spring Framework release.

3.2 Removed Deprecated Packages and Methods

All deprecated packages, and many deprecated classes and methods have been removed with version

4.0. If you are upgrading from a previous release of Spring, you should ensure that you have fixed any

deprecated calls that you were making to outdated APIs.

For a complete set of changes, check out the API Differences Report.

Note that optional third-party dependencies have been raised to a 2010/2011 minimum (i.e. Spring 4

generally only supports versions released in late 2010 or later now): notably, Hibernate 3.6+, EhCache

2.1+, Quartz 1.8+, Groovy 1.8+, and Joda-Time 2.0+. As an exception to the rule, Spring 4 requires the

recent Hibernate Validator 4.3+, and support for Jackson has been focused on 2.0+ now (with Jackson

1.8/1.9 support retained for the time being where Spring 3.2 had it; now just in deprecated form).

3.3 Java 8 (as well as 6 and 7)

Spring Framework 4.0 provides support for several Java 8 features. You can make use of lambda

expressions and method references with Spring’s callback interfaces. There is first-class support for

java.time (JSR-310), and several existing annotations have been retrofitted as @Repeatable. You

can also use Java 8’s parameter name discovery (based on the -parameters compiler flag) as an

alternative to compiling your code with debug information enabled.

Spring remains compatible with older versions of Java and the JDK: concretely, Java SE 6 (specifically,

a minimum level equivalent to JDK 6 update 18, as released in January 2010) and above are still fully

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 18

supported. However, for newly started development projects based on Spring 4, we recommend the

use of Java 7 or 8.

3.4 Java EE 6 and 7

Java EE version 6 or above is now considered the baseline for Spring Framework 4, with the JPA 2.0

and Servlet 3.0 specifications being of particular relevance. In order to remain compatible with Google

App Engine and older application servers, it is possible to deploy a Spring 4 application into a Servlet

2.5 environment. However, Servlet 3.0+ is strongly recommended and a prerequisite in Spring’s test

and mock packages for test setups in development environments.

Note

If you are a WebSphere 7 user, be sure to install the JPA 2.0 feature pack. On WebLogic 10.3.4

or higher, install the JPA 2.0 patch that comes with it. This turns both of those server generations

into Spring 4 compatible deployment environments.

On a more forward-looking note, Spring Framework 4.0 supports the Java EE 7 level of applicable

specifications now: in particular, JMS 2.0, JTA 1.2, JPA 2.1, Bean Validation 1.1, and JSR-236

Concurrency Utilities. As usual, this support focuses on individual use of those specifications, e.g. on

Tomcat or in standalone environments. However, it works equally well when a Spring application is

deployed to a Java EE 7 server.

Note that Hibernate 4.3 is a JPA 2.1 provider and therefore only supported as of Spring Framework 4.0.

The same applies to Hibernate Validator 5.0 as a Bean Validation 1.1 provider. Neither of the two are

officially supported with Spring Framework 3.2.

3.5 Groovy Bean Definition DSL

With Spring Framework 4.0 it is now possible to define external bean configuration using a Groovy DSL.

This is similar in concept to using XML bean definitions, but allows for a more concise syntax. Using

Groovy also allows you to easily embed bean definitions directly in your bootstrap code. For example:

def reader = new GroovyBeanDefinitionReader(myApplicationContext)

reader.beans {

dataSource(BasicDataSource) {

driverClassName = "org.hsqldb.jdbcDriver"

url = "jdbc:hsqldb:mem:grailsDB"

username = "sa"

password = ""

settings = [mynew:"setting"]

}

sessionFactory(SessionFactory) {

dataSource = dataSource

}

myService(MyService) {

nestedBean = { AnotherBean bean ->

dataSource = dataSource

}

For more information consult the GroovyBeanDefinitionReader javadocs.

3.6 Core Container Improvements

There have been several general improvements to the core container:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 19

• Spring now treats generic types as a form of qualifier when injecting Beans. For example, if you are

using a Spring Data Repository you can now easily inject a specific implementation: @Autowired

Repository<Customer> customerRepository.

• If you use Spring’s meta-annotation support, you can now develop custom annotations that expose

specific attributes from the source annotation.

• Beans can now be ordered when they are autowired into lists and arrays. Both the @Order annotation

and Ordered interface are supported.

• The @Lazy annotation can now be used on injection points, as well as on @Bean definitions.

• The @Description annotation has been introduced for developers using Java-based configuration.

• A generalized model for conditionally filtering beans has been added via the @Conditional

annotation. This is similar to @Profile support but allows for user-defined strategies to be developed

programmatically.

•CGLIB-based proxy classes no longer require a default constructor. Support is provided via the

objenesis library which is repackaged inline and distributed as part of the Spring Framework. With

this strategy, no constructor at all is being invoked for proxy instances anymore.

• There is managed time zone support across the framework now, e.g. on LocaleContext.

3.7 General Web Improvements

Deployment to Servlet 2.5 servers remains an option, but Spring Framework 4.0 is now focused primarily

on Servlet 3.0+ environments. If you are using the Spring MVC Test Framework you will need to ensure

that a Servlet 3.0 compatible JAR is in your test classpath.

In addition to the WebSocket support mentioned later, the following general improvements have been

made to Spring’s Web modules:

• You can use the new @RestController annotation with Spring MVC applications, removing the

need to add @ResponseBody to each of your @RequestMapping methods.

• The AsyncRestTemplate class has been added, allowing non-blocking asynchronous support

when developing REST clients.

• Spring now offers comprehensive timezone support when developing Spring MVC applications.

3.8 WebSocket, SockJS, and STOMP Messaging

A new spring-websocket module provides comprehensive support for WebSocket-based, two-way

communication between client and server in web applications. It is compatible with JSR-356, the Java

WebSocket API, and in addition provides SockJS-based fallback options (i.e. WebSocket emulation)

for use in browsers that don’t yet support the WebSocket protocol (e.g. Internet Explorer < 10).

A new spring-messaging module adds support for STOMP as the WebSocket sub-protocol to use in

applications along with an annotation programming model for routing and processing STOMP messages

from WebSocket clients. As a result an @Controller can now contain both @RequestMapping and

@MessageMapping methods for handling HTTP requests and messages from WebSocket-connected

clients. The new spring-messaging module also contains key abstractions formerly from the Spring

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 20

Integration project such as Message, MessageChannel, MessageHandler, and others to serve as

a foundation for messaging-based applications.

For further details, including a more thorough introduction, see the Chapter 21, WebSocket Support

section.

3.9 Testing Improvements

In addition to pruning of deprecated code within the spring-test module, Spring Framework 4.0

introduces several new features for use in unit and integration testing.

• Almost all annotations in the spring-test module (e.g., @ContextConfiguration,

@WebAppConfiguration, @ContextHierarchy, @ActiveProfiles, etc.) can now be used

as meta-annotations to create custom composed annotations and reduce configuration duplication

across a test suite.

• Active bean definition profiles can now be resolved programmatically, simply by implementing

a custom ActiveProfilesResolver and registering it via the resolver attribute of

@ActiveProfiles.

• A new SocketUtils class has been introduced in the spring-core module which enables you to

scan for free TCP and UDP server ports on localhost. This functionality is not specific to testing but

can prove very useful when writing integration tests that require the use of sockets, for example tests

that start an in-memory SMTP server, FTP server, Servlet container, etc.

• As of Spring 4.0, the set of mocks in the org.springframework.mock.web package is

now based on the Servlet 3.0 API. Furthermore, several of the Servlet API mocks (e.g.,

MockHttpServletRequest, MockServletContext, etc.) have been updated with minor

enhancements and improved configurability.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 21

4. New Features and Enhancements in Spring

Framework 4.1

4.1 JMS Improvements

Spring 4.1 introduces a much simpler infrastructure to register JMS listener endpoints by annotating

bean methods with @JmsListener. The XML namespace has been enhanced to support this new

style (jms:annotation-driven), and it is also possible to fully configure the infrastructure using

Java config (@EnableJms, JmsListenerContainerFactory). It is also possible to register listener

endpoints programmatically using JmsListenerConfigurer.

Spring 4.1 also aligns its JMS support to allow you to benefit from the spring-messaging abstraction

introduced in 4.0, that is:

• Message listener endpoints can have a more flexible signature and benefit from standard messaging

annotations such as @Payload, @Header, @Headers, and @SendTo. It is also possible to use a

standard Message in lieu of javax.jms.Message as method argument.

• A new JmsMessageOperations interface is available and permits JmsTemplate like operations

using the Message abstraction.

Finally, Spring 4.1 provides additional miscellaneous improvements:

• Synchronous request-reply operations support in JmsTemplate

• Listener priority can be specified per <jms:listener/> element

• Recovery options for the message listener container are configurable using a BackOff

implementation

• JMS 2.0 shared consumers are supported

4.2 Caching Improvements

Spring 4.1 supports JCache (JSR-107) annotations using Spring’s existing cache configuration and

infrastructure abstraction; no changes are required to use the standard annotations.

Spring 4.1 also improves its own caching abstraction significantly:

• Caches can be resolved at runtime using a CacheResolver. As a result the value argument

defining the cache name(s) to use is no longer mandatory.

• More operation-level customizations: cache resolver, cache manager, key generator

• A new @CacheConfig class-level annotation allows common settings to be shared at the class level

without enabling any cache operation.

• Better exception handling of cached methods using CacheErrorHandler

Spring 4.1 also has a breaking change in the CacheInterface as a new putIfAbsent method has

been added.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 22

4.3 Web Improvements

• The existing support for resource handling based on the ResourceHttpRequestHandler

has been expanded with new abstractions ResourceResolver, ResourceTransformer, and

ResourceUrlProvider. A number of built-in implementations provide support for versioned

resource URLs (for effective HTTP caching), locating gzipped resources, generating an HTML 5

AppCache manifests, and more. See the section called “Serving of Resources”.

• JDK 1.8’s java.util.Optional is now supported for @RequestParam, @RequestHeader, and

@MatrixVariable controller method arguments.

•ListenableFuture is supported as a return value alternative to DeferredResult

where an underlying service (or perhaps a call to AsyncRestTemplate) already returns

ListenableFuture.

•@ModelAttribute methods are now invoked in an order that respects inter-dependencies. See

jira.springsource.org/browse/SPR-6299[SPR-6299].

• Jackson’s @JsonView is supported directly on @ResponseBody and ResponseEntity controller

methods for serializing different amounts of detail for the same POJO (e.g. summary vs. detail page).

This is also supported with View-based rendering by adding the serialization view type as a model

attribute under a special key. See the section called “Jackson Serialization View Support” for details.

• JSONP is now supported with Jackson. See the section called “Jackson JSONP Support”.

• A new lifecycle option is available for intercepting @ResponseBody and ResponseEntity methods

just after the controller method returns and before the response is written. To take advantage declare

an @ControllerAdvice bean that implements ResponseBodyAdvice. The built-in support for

@JsonView and JSONP take advantage of this. See the section called “Intercepting requests with

a HandlerInterceptor”.

• There are three new HttpMessageConverter options:

• Gson — lighter footprint than Jackson; has already been in use in Spring Android.

• Google Protocol Buffers — efficient and effective as an inter-service communication data protocol

within an enterprise but can also be exposed as JSON and XML for browsers.

• Jackson based XML serialization is now supported through the jackson-dataformat-xml extension.

When using @EnableWebMvc or <mvc:annotation-driven/>, this is used by default instead

of JAXB2 if jackson-dataformat-xml is in the classpath.

• Views such as JSPs can now build links to controllers by referring to controller mappings by name. A

default name is assigned to every @RequestMapping. For example FooController with method

handleFoo is named "FC#handleFoo". The naming strategy is pluggable. It is also possible to name

an @RequestMapping explicitly through its name attribute. A new mvcUrl function in the Spring JSP

tag library makes this easy to use in JSP pages. See the section called “Building URIs to Controllers

and methods from views”.

•ResponseEntity provides a builder-style API to guide controller methods towards the preparation

of server-side responses, e.g. ResponseEntity.ok().

•RequestEntity is a new type that provides a builder-style API to guide client-side REST code

towards the preparation of HTTP requests.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 23

• MVC Java config and XML namespace:

• View resolvers can now be configured including support for content negotiation, see the section

called “View Resolvers”.

• View controllers now have built-in support for redirects and for setting the response status. An

application can use this to configure redirect URLs, render 404 responses with a view, send "no

content" responses, etc. Some use cases are listed here.

• Path matching customizations are frequently used and now built-in. See the section called “Path

Matching”.

•Groovy markup template support (based on Groovy 2.3). See the GroovyMarkupConfigurer and

respecitve ViewResolver and ‘View’ implementations.

4.4 WebSocket STOMP Messaging Improvements

• SockJS (Java) client-side support. See SockJsClient and classes in same package.

• New application context events SessionSubscribeEvent and SessionUnubscribeEvent

published when STOMP clients subscribe and unsubscribe.

• New "websocket" scope. See the section called “WebSocket Scope”.

•@SendToUser can target only a single session and does not require an authenticated user.

•@MessageMapping methods can use dot "." instead of slash "/" as path separator. See SPR-11660.

• STOMP/WebSocket monitoring info collected and logged. See the section called “Runtime

Monitoring”.

• Significantly optimized and improved logging that should remain very readable and compact even at

DEBUG level.

• Optimized message creation including support for temporary message mutability and avoiding

automatic message id and timestamp creation. See Javadoc of MessageHeaderAccessor.

• STOMP/WebSocket connections that have not activity 60 seconds after the WebSocket session is

established. See jira.springsource.org/browse/SPR-11884[SPR-11884].

4.5 Testing Improvements

• Groovy scripts can now be used to configure the ApplicationContext loaded for integration tests

in the TestContext framework.

• See the section called “Context configuration with Groovy scripts” for details.

• Test-managed transactions can now be programmatically started and ended within transactional test

methods via the new TestTransaction API.

• See the section called “Programmatic transaction management” for details.

• SQL script execution can now be configured declaratively via the new @Sql and @SqlConfig

annotations on a per-class or per-method basis.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 24

• See the section called “Executing SQL scripts” for details.

• Test property sources which automatically override system and application property sources can be

configured via the new @TestPropertySource annotation.

• See the section called “Context configuration with test property sources” for details.

• Default TestExecutionListeners can now be automatically discovered.

• See the section called “Automatic discovery of default TestExecutionListeners” for details.

• Custom TestExecutionListeners can now be automatically merged with the default listeners.

• See the section called “Merging TestExecutionListeners” for details.

• The documentation for transactional testing support in the TestContext framework has been improved

with more thorough explanations and additional examples.

• See the section called “Transaction management” for details.

• Various improvements to MockServletContext, MockHttpServletRequest, and other Servlet

API mocks.

•AssertThrows has been refactored to support Throwable instead of Exception.

• In Spring MVC Test, JSON responses can be asserted with JSON Assert as an extra option to using

JSONPath much like it has been possible to do for XML with XMLUnit.

•MockMvcBuilder recipes can now be created with the help of MockMvcConfigurer. This was

added to make it easy to apply Spring Security setup but can be used to encapsulate common setup

for any 3rd party framework or within a project.

•MockRestServiceServer now supports the AsyncRestTemplate for client-side testing.

Part III. Core Technologies

This part of the reference documentation covers all of those technologies that are absolutely integral

to the Spring Framework.

Foremost amongst these is the Spring Framework’s Inversion of Control (IoC) container. A thorough

treatment of the Spring Framework’s IoC container is closely followed by comprehensive coverage of

Spring’s Aspect-Oriented Programming (AOP) technologies. The Spring Framework has its own AOP

framework, which is conceptually easy to understand, and which successfully addresses the 80% sweet

spot of AOP requirements in Java enterprise programming.

Coverage of Spring’s integration with AspectJ (currently the richest - in terms of features - and certainly

most mature AOP implementation in the Java enterprise space) is also provided.

Finally, the adoption of the test-driven-development (TDD) approach to software development is

certainly advocated by the Spring team, and so coverage of Spring’s support for integration testing is

covered (alongside best practices for unit testing). The Spring team has found that the correct use of

IoC certainly does make both unit and integration testing easier (in that the presence of setter methods

and appropriate constructors on classes makes them easier to wire together in a test without having

to set up service locator registries and suchlike)… the chapter dedicated solely to testing will hopefully

convince you of this as well.

• Chapter 5, The IoC container

• Chapter 6, Resources

• Chapter 7, Validation, Data Binding, and Type Conversion

• Chapter 8, Spring Expression Language (SpEL)

• Chapter 9, Aspect Oriented Programming with Spring

• Chapter 10, Spring AOP APIs

• Chapter 11, Testing

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 26

5. The IoC container

5.1 Introduction to the Spring IoC container and beans

This chapter covers the Spring Framework implementation of the Inversion of Control (IoC) 1 principle.

IoC is also known as dependency injection (DI). It is a process whereby objects define their

dependencies, that is, the other objects they work with, only through constructor arguments, arguments

to a factory method, or properties that are set on the object instance after it is constructed or returned

from a factory method. The container then injects those dependencies when it creates the bean. This

process is fundamentally the inverse, hence the name Inversion of Control (IoC), of the bean itself

controlling the instantiation or location of its dependencies by using direct construction of classes, or a

mechanism such as the Service Locator pattern.

The org.springframework.beans and org.springframework.context packages are the

basis for Spring Framework’s IoC container. The BeanFactory interface provides an advanced

configuration mechanism capable of managing any type of object. ApplicationContext is a sub-

interface of BeanFactory. It adds easier integration with Spring’s AOP features; message resource

handling (for use in internationalization), event publication; and application-layer specific contexts such

as the WebApplicationContext for use in web applications.

In short, the BeanFactory provides the configuration framework and basic functionality, and the

ApplicationContext adds more enterprise-specific functionality. The ApplicationContext is

a complete superset of the BeanFactory, and is used exclusively in this chapter in descriptions

of Spring’s IoC container. For more information on using the BeanFactory instead of the

ApplicationContext, refer to Section 5.16, “The BeanFactory”.

In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC

container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed

by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application. Beans,

and the dependencies among them, are reflected in the configuration metadata used by a container.

5.2 Container overview

The interface org.springframework.context.ApplicationContext represents the Spring IoC

container and is responsible for instantiating, configuring, and assembling the aforementioned beans.

The container gets its instructions on what objects to instantiate, configure, and assemble by reading

configuration metadata. The configuration metadata is represented in XML, Java annotations, or Java

code. It allows you to express the objects that compose your application and the rich interdependencies

between such objects.

Several implementations of the ApplicationContext interface are supplied out-of-the-

box with Spring. In standalone applications it is common to create an instance of

ClassPathXmlApplicationContext or FileSystemXmlApplicationContext. While XML has

been the traditional format for defining configuration metadata you can instruct the container to use

Java annotations or code as the metadata format by providing a small amount of XML configuration to

declaratively enable support for these additional metadata formats.

In most application scenarios, explicit user code is not required to instantiate one or more instances

of a Spring IoC container. For example, in a web application scenario, a simple eight (or so) lines

1See Background

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 27

of boilerplate web descriptor XML in the web.xml file of the application will typically suffice (see the

section called “Convenient ApplicationContext instantiation for web applications”). If you are using the

Spring Tool Suite Eclipse-powered development environment this boilerplate configuration can be easily

created with few mouse clicks or keystrokes.

The following diagram is a high-level view of how Spring works. Your application classes are combined

with configuration metadata so that after the ApplicationContext is created and initialized, you have

a fully configured and executable system or application.

Figure 5.1. The Spring IoC container

Configuration metadata

As the preceding diagram shows, the Spring IoC container consumes a form of configuration metadata;

this configuration metadata represents how you as an application developer tell the Spring container to

instantiate, configure, and assemble the objects in your application.

Configuration metadata is traditionally supplied in a simple and intuitive XML format, which is what most

of this chapter uses to convey key concepts and features of the Spring IoC container.

Note

XML-based metadata is not the only allowed form of configuration metadata. The Spring IoC

container itself is totally decoupled from the format in which this configuration metadata is

actually written. These days many developers choose Java-based configuration for their Spring

applications.

For information about using other forms of metadata with the Spring container, see:

•Annotation-based configuration: Spring 2.5 introduced support for annotation-based configuration

metadata.

•Java-based configuration: Starting with Spring 3.0, many features provided by the Spring JavaConfig

project became part of the core Spring Framework. Thus you can define beans external to your

application classes by using Java rather than XML files. To use these new features, see the

@Configuration, @Bean, @Import and @DependsOn annotations.

Spring configuration consists of at least one and typically more than one bean definition that the

container must manage. XML-based configuration metadata shows these beans configured as <bean/

> elements inside a top-level <beans/> element. Java configuration typically uses @Bean annotated

methods within a @Configuration class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 28

These bean definitions correspond to the actual objects that make up your application. Typically you

define service layer objects, data access objects (DAOs), presentation objects such as Struts Action

instances, infrastructure objects such as Hibernate SessionFactories, JMS Queues, and so forth.

Typically one does not configure fine-grained domain objects in the container, because it is usually the

responsibility of DAOs and business logic to create and load domain objects. However, you can use

Spring’s integration with AspectJ to configure objects that have been created outside the control of an

IoC container. See Using AspectJ to dependency-inject domain objects with Spring.

The following example shows the basic structure of XML-based configuration metadata:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

</bean>

</bean>

</beans>

The id attribute is a string that you use to identify the individual bean definition. The class attribute

defines the type of the bean and uses the fully qualified classname. The value of the id attribute refers

to collaborating objects. The XML for referring to collaborating objects is not shown in this example; see

Dependencies for more information.

Instantiating a container

Instantiating a Spring IoC container is straightforward. The location path or paths supplied to an

ApplicationContext constructor are actually resource strings that allow the container to load

configuration metadata from a variety of external resources such as the local file system, from the Java

CLASSPATH, and so on.

ApplicationContext context =

new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});

Note

After you learn about Spring’s IoC container, you may want to know more about Spring’s

Resource abstraction, as described in Chapter 6, Resources, which provides a convenient

mechanism for reading an InputStream from locations defined in a URI syntax. In particular,

Resource paths are used to construct applications contexts as described in Section 6.7,

“Application contexts and Resource paths”.

The following example shows the service layer objects (services.xml) configuration file:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 29

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

</bean>

</beans>

The following example shows the data access objects daos.xml file:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="accountDao"

class="org.springframework.samples.jpetstore.dao.jpa.JpaAccountDao">

</bean>

</bean>

</beans>

In the preceding example, the service layer consists of the class PetStoreServiceImpl, and two data

access objects of the type JpaAccountDao and JpaItemDao (based on the JPA Object/Relational

mapping standard). The property name element refers to the name of the JavaBean property,

and the ref element refers to the name of another bean definition. This linkage between id and

ref elements expresses the dependency between collaborating objects. For details of configuring an

object’s dependencies, see Dependencies.

Composing XML-based configuration metadata

It can be useful to have bean definitions span multiple XML files. Often each individual XML configuration

file represents a logical layer or module in your architecture.

You can use the application context constructor to load bean definitions from all these XML fragments.

This constructor takes multiple Resource locations, as was shown in the previous section. Alternatively,

use one or more occurrences of the <import/> element to load bean definitions from another file or

files. For example:

<beans>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 30

In the preceding example, external bean definitions are loaded from three files: services.xml,

messageSource.xml, and themeSource.xml. All location paths are relative to the definition file

doing the importing, so services.xml must be in the same directory or classpath location as the file

doing the importing, while messageSource.xml and themeSource.xml must be in a resources

location below the location of the importing file. As you can see, a leading slash is ignored, but given

that these paths are relative, it is better form not to use the slash at all. The contents of the files being

imported, including the top level <beans/> element, must be valid XML bean definitions according to

the Spring Schema.

Note

It is possible, but not recommended, to reference files in parent directories using a relative

"../" path. Doing so creates a dependency on a file that is outside the current application. In

particular, this reference is not recommended for "classpath:" URLs (for example, "classpath:../

services.xml"), where the runtime resolution process chooses the "nearest" classpath root and

then looks into its parent directory. Classpath configuration changes may lead to the choice of a

different, incorrect directory.

You can always use fully qualified resource locations instead of relative paths: for example, "file:C:/

config/services.xml" or "classpath:/config/services.xml". However, be aware that you are coupling

your application’s configuration to specific absolute locations. It is generally preferable to keep an

indirection for such absolute locations, for example, through "${…}" placeholders that are resolved

against JVM system properties at runtime.

Using the container

The ApplicationContext is the interface for an advanced factory capable of maintaining a registry

of different beans and their dependencies. Using the method T getBean(String name, Class<T>

requiredType) you can retrieve instances of your beans.

The ApplicationContext enables you to read bean definitions and access them as follows:

// create and configure beans

ApplicationContext context =

new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});

// retrieve configured instance

PetStoreService service = context.getBean("petStore", PetStoreService.class);

// use configured instance

List<String> userList = service.getUsernameList();

You use getBean() to retrieve instances of your beans. The ApplicationContext interface has a

few other methods for retrieving beans, but ideally your application code should never use them. Indeed,

your application code should have no calls to the getBean() method at all, and thus no dependency

on Spring APIs at all. For example, Spring’s integration with web frameworks provides for dependency

injection for various web framework classes such as controllers and JSF-managed beans.

5.3 Bean overview

A Spring IoC container manages one or more beans. These beans are created with the configuration

metadata that you supply to the container, for example, in the form of XML <bean/> definitions.

Within the container itself, these bean definitions are represented as BeanDefinition objects, which

contain (among other information) the following metadata:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 31

•A package-qualified class name: typically the actual implementation class of the bean being defined.

• Bean behavioral configuration elements, which state how the bean should behave in the container

(scope, lifecycle callbacks, and so forth).

• References to other beans that are needed for the bean to do its work; these references are also

called collaborators or dependencies.

• Other configuration settings to set in the newly created object, for example, the number of connections

to use in a bean that manages a connection pool, or the size limit of the pool.

This metadata translates to a set of properties that make up each bean definition.

Table 5.1. The bean definition

Property Explained in…

class the section called “Instantiating beans”

name the section called “Naming beans”

scope Section 5.5, “Bean scopes”

constructor arguments the section called “Dependency injection”

properties the section called “Dependency injection”

autowiring mode the section called “Autowiring collaborators”

lazy-initialization mode the section called “Lazy-initialized beans”

initialization method the section called “Initialization callbacks”

destruction method the section called “Destruction callbacks”

In addition to bean definitions that contain information on how to create a specific bean, the

ApplicationContext implementations also permit the registration of existing objects that are

created outside the container, by users. This is done by accessing the ApplicationContext’s

BeanFactory via the method getBeanFactory() which returns the BeanFactory implementation

DefaultListableBeanFactory. DefaultListableBeanFactory supports this registration

through the methods registerSingleton(..) and registerBeanDefinition(..). However,

typical applications work solely with beans defined through metadata bean definitions.

Naming beans

Every bean has one or more identifiers. These identifiers must be unique within the container that hosts

the bean. A bean usually has only one identifier, but if it requires more than one, the extra ones can

be considered aliases.

In XML-based configuration metadata, you use the id and/or name attributes to specify the bean

identifier(s). The id attribute allows you to specify exactly one id. Conventionally these names are

alphanumeric (myBean, fooService, etc.), but may contain special characters as well. If you want to

introduce other aliases to the bean, you can also specify them in the name attribute, separated by a

comma (,), semicolon (;), or white space. As a historical note, in versions prior to Spring 3.1, the id

attribute was defined as an xsd:ID type, which constrained possible characters. As of 3.1, it is defined

as an xsd:string type. Note that bean id uniqueness is still enforced by the container, though no

longer by XML parsers.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 32

You are not required to supply a name or id for a bean. If no name or id is supplied explicitly, the container

generates a unique name for that bean. However, if you want to refer to that bean by name, through the

use of the ref element or Service Locator style lookup, you must provide a name. Motivations for not

supplying a name are related to using inner beans and autowiring collaborators.

Bean Naming Conventions

The convention is to use the standard Java convention for instance field names when naming

beans. That is, bean names start with a lowercase letter, and are camel-cased from then on.

Examples of such names would be (without quotes) 'accountManager', 'accountService',

'userDao', 'loginController', and so forth.

Naming beans consistently makes your configuration easier to read and understand, and if you

are using Spring AOP it helps a lot when applying advice to a set of beans related by name.

Aliasing a bean outside the bean definition

In a bean definition itself, you can supply more than one name for the bean, by using a combination

of up to one name specified by the id attribute, and any number of other names in the name attribute.

These names can be equivalent aliases to the same bean, and are useful for some situations, such as

allowing each component in an application to refer to a common dependency by using a bean name

that is specific to that component itself.

Specifying all aliases where the bean is actually defined is not always adequate, however. It is

sometimes desirable to introduce an alias for a bean that is defined elsewhere. This is commonly the

case in large systems where configuration is split amongst each subsystem, each subsystem having its

own set of object definitions. In XML-based configuration metadata, you can use the <alias/> element

to accomplish this.

In this case, a bean in the same container which is named fromName, may also, after the use of this

alias definition, be referred to as toName.

For example, the configuration metadata for subsystem A may refer to a DataSource via the name

subsystemA-dataSource. The configuration metadata for subsystem B may refer to a DataSource

via the name subsystemB-dataSource. When composing the main application that uses both these

subsystems the main application refers to the DataSource via the name myApp-dataSource. To have

all three names refer to the same object you add to the MyApp configuration metadata the following

aliases definitions:

Now each component and the main application can refer to the dataSource through a name that is

unique and guaranteed not to clash with any other definition (effectively creating a namespace), yet

they refer to the same bean.

Java-configuration

If you are using Java-configuration, the @Bean annotation can be used to provide aliases see the

section called “Using the @Bean annotation” for details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 33

Instantiating beans

A bean definition essentially is a recipe for creating one or more objects. The container looks at the

recipe for a named bean when asked, and uses the configuration metadata encapsulated by that bean

definition to create (or acquire) an actual object.

If you use XML-based configuration metadata, you specify the type (or class) of object that is to be

instantiated in the class attribute of the <bean/> element. This class attribute, which internally is a

Class property on a BeanDefinition instance, is usually mandatory. (For exceptions, see the section

called “Instantiation using an instance factory method” and Section 5.7, “Bean definition inheritance”.)

You use the Class property in one of two ways:

• Typically, to specify the bean class to be constructed in the case where the container itself directly

creates the bean by calling its constructor reflectively, somewhat equivalent to Java code using the

new operator.

• To specify the actual class containing the static factory method that will be invoked to create the

object, in the less common case where the container invokes a static factory method on a class

to create the bean. The object type returned from the invocation of the static factory method may

be the same class or another class entirely.

Inner class names. If you want to configure a bean definition for a static nested class, you

have to use the binary name of the inner class.

For example, if you have a class called Foo in the com.example package, and this Foo class

has a static inner class called Bar, the value of the 'class' attribute on a bean definition

would be…

com.example.Foo$Bar

Notice the use of the $ character in the name to separate the inner class name from the outer

class name.

Instantiation with a constructor

When you create a bean by the constructor approach, all normal classes are usable by and compatible

with Spring. That is, the class being developed does not need to implement any specific interfaces or

to be coded in a specific fashion. Simply specifying the bean class should suffice. However, depending

on what type of IoC you use for that specific bean, you may need a default (empty) constructor.

The Spring IoC container can manage virtually any class you want it to manage; it is not limited to

managing true JavaBeans. Most Spring users prefer actual JavaBeans with only a default (no-argument)

constructor and appropriate setters and getters modeled after the properties in the container. You can

also have more exotic non-bean-style classes in your container. If, for example, you need to use a legacy

connection pool that absolutely does not adhere to the JavaBean specification, Spring can manage it

as well.

With XML-based configuration metadata you can specify your bean class as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 34

For details about the mechanism for supplying arguments to the constructor (if required) and setting

object instance properties after the object is constructed, see Injecting Dependencies.

Instantiation with a static factory method

When defining a bean that you create with a static factory method, you use the class attribute to specify

the class containing the static factory method and an attribute named factory-method to specify

the name of the factory method itself. You should be able to call this method (with optional arguments as

described later) and return a live object, which subsequently is treated as if it had been created through

a constructor. One use for such a bean definition is to call static factories in legacy code.

The following bean definition specifies that the bean will be created by calling a factory-method. The

definition does not specify the type (class) of the returned object, only the class containing the factory

method. In this example, the createInstance() method must be a static method.

<bean id="clientService"

class="examples.ClientService"

factory-method="createInstance"/>

public class ClientService {

private static ClientService clientService = new ClientService();

private ClientService() {}

public static ClientService createInstance() {

return clientService;

}

For details about the mechanism for supplying (optional) arguments to the factory method and

setting object instance properties after the object is returned from the factory, see Dependencies and

configuration in detail.

Instantiation using an instance factory method

Similar to instantiation through a static factory method, instantiation with an instance factory method

invokes a non-static method of an existing bean from the container to create a new bean. To use this

mechanism, leave the class attribute empty, and in the factory-bean attribute, specify the name of a

bean in the current (or parent/ancestor) container that contains the instance method that is to be invoked

to create the object. Set the name of the factory method itself with the factory-method attribute.

</bean>

<bean id="clientService"

factory-bean="serviceLocator"

factory-method="createClientServiceInstance"/>

public class DefaultServiceLocator {

private static ClientService clientService = new ClientServiceImpl();

private DefaultServiceLocator() {}

public ClientService createClientServiceInstance() {

return clientService;

}

One factory class can also hold more than one factory method as shown here:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 35

</bean>

<bean id="clientService"

factory-bean="serviceLocator"

factory-method="createClientServiceInstance"/>

<bean id="accountService"

factory-bean="serviceLocator"

factory-method="createAccountServiceInstance"/>

public class DefaultServiceLocator {

private static ClientService clientService = new ClientServiceImpl();

private static AccountService accountService = new AccountServiceImpl();

private DefaultServiceLocator() {}

public ClientService createClientServiceInstance() {

return clientService;

}

public AccountService createAccountServiceInstance() {

return accountService;

}

This approach shows that the factory bean itself can be managed and configured through dependency

injection (DI). See Dependencies and configuration in detail.

Note

In Spring documentation, factory bean refers to a bean that is configured in the Spring container

that will create objects through an instance or static factory method. By contrast, FactoryBean

(notice the capitalization) refers to a Spring-specific FactoryBean.

5.4 Dependencies

A typical enterprise application does not consist of a single object (or bean in the Spring parlance). Even

the simplest application has a few objects that work together to present what the end-user sees as a

coherent application. This next section explains how you go from defining a number of bean definitions

that stand alone to a fully realized application where objects collaborate to achieve a goal.

Dependency injection

Dependency injection (DI) is a process whereby objects define their dependencies, that is, the other

objects they work with, only through constructor arguments, arguments to a factory method, or properties

that are set on the object instance after it is constructed or returned from a factory method. The container

then injects those dependencies when it creates the bean. This process is fundamentally the inverse,

hence the name Inversion of Control (IoC), of the bean itself controlling the instantiation or location of

its dependencies on its own by using direct construction of classes, or the Service Locator pattern.

Code is cleaner with the DI principle and decoupling is more effective when objects are provided with

their dependencies. The object does not look up its dependencies, and does not know the location

or class of the dependencies. As such, your classes become easier to test, in particular when the

dependencies are on interfaces or abstract base classes, which allow for stub or mock implementations

to be used in unit tests.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 36

DI exists in two major variants, Constructor-based dependency injection and Setter-based dependency

injection.

Constructor-based dependency injection

Constructor-based DI is accomplished by the container invoking a constructor with a number of

arguments, each representing a dependency. Calling a static factory method with specific arguments

to construct the bean is nearly equivalent, and this discussion treats arguments to a constructor and to

a static factory method similarly. The following example shows a class that can only be dependency-

injected with constructor injection. Notice that there is nothing special about this class, it is a POJO that

has no dependencies on container specific interfaces, base classes or annotations.

public class SimpleMovieLister {

// the SimpleMovieLister has a dependency on a MovieFinder

private MovieFinder movieFinder;

// a constructor so that the Spring container can inject a MovieFinder

public SimpleMovieLister(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// business logic that actually uses the injected MovieFinder is omitted...

}

Constructor argument resolution

Constructor argument resolution matching occurs using the argument’s type. If no potential ambiguity

exists in the constructor arguments of a bean definition, then the order in which the constructor

arguments are defined in a bean definition is the order in which those arguments are supplied to the

appropriate constructor when the bean is being instantiated. Consider the following class:

package x.y;

public class Foo {

public Foo(Bar bar, Baz baz) {

// ...

}

No potential ambiguity exists, assuming that Bar and Baz classes are not related by inheritance. Thus

the following configuration works fine, and you do not need to specify the constructor argument indexes

and/or types explicitly in the <constructor-arg/> element.

<beans>

<constructor-arg ref="bar"/>

<constructor-arg ref="baz"/>

</bean>

</beans>

When another bean is referenced, the type is known, and matching can occur (as was the case with

the preceding example). When a simple type is used, such as <value>true</value>, Spring cannot

determine the type of the value, and so cannot match by type without help. Consider the following class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 37

package examples;

public class ExampleBean {

// Number of years to calculate the Ultimate Answer

private int years;

// The Answer to Life, the Universe, and Everything

private String ultimateAnswer;

public ExampleBean(int years, String ultimateAnswer) {

this.years = years;

this.ultimateAnswer = ultimateAnswer;

}

In the preceding scenario, the container can use type matching with simple types if you explicitly specify

the type of the constructor argument using the type attribute. For example:

<constructor-arg type="int" value="7500000"/>

<constructor-arg type="java.lang.String" value="42"/>

</bean>

Use the index attribute to specify explicitly the index of constructor arguments. For example:

<constructor-arg index="0" value="7500000"/>

<constructor-arg index="1" value="42"/>

</bean>

In addition to resolving the ambiguity of multiple simple values, specifying an index resolves ambiguity

where a constructor has two arguments of the same type. Note that the index is 0 based.

You can also use the constructor parameter name for value disambiguation:

<constructor-arg name="years" value="7500000"/>

<constructor-arg name="ultimateAnswer" value="42"/>

</bean>

Keep in mind that to make this work out of the box your code must be compiled with the debug flag

enabled so that Spring can look up the parameter name from the constructor. If you can’t compile your

code with debug flag (or don’t want to) you can use @ConstructorProperties JDK annotation to explicitly

name your constructor arguments. The sample class would then have to look as follows:

package examples;

public class ExampleBean {

// Fields omitted

@ConstructorProperties({"years", "ultimateAnswer"})

public ExampleBean(int years, String ultimateAnswer) {

this.years = years;

this.ultimateAnswer = ultimateAnswer;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 38

Setter-based dependency injection

Setter-based DI is accomplished by the container calling setter methods on your beans after invoking a

no-argument constructor or no-argument static factory method to instantiate your bean.

The following example shows a class that can only be dependency-injected using pure setter injection.

This class is conventional Java. It is a POJO that has no dependencies on container specific interfaces,

base classes or annotations.

public class SimpleMovieLister {

// the SimpleMovieLister has a dependency on the MovieFinder

private MovieFinder movieFinder;

// a setter method so that the Spring container can inject a MovieFinder

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// business logic that actually uses the injected MovieFinder is omitted...

}

The ApplicationContext supports constructor-based and setter-based DI for the beans it manages.

It also supports setter-based DI after some dependencies have already been injected through the

constructor approach. You configure the dependencies in the form of a BeanDefinition, which

you use in conjunction with PropertyEditor instances to convert properties from one format to

another. However, most Spring users do not work with these classes directly (i.e., programmatically) but

rather with XML bean definitions, annotated components (i.e., classes annotated with @Component,

@Controller, etc.), or @Bean methods in Java-based @Configuration classes. These sources are

then converted internally into instances of BeanDefinition and used to load an entire Spring IoC

container instance.

Constructor-based or setter-based DI?

Since you can mix constructor-based and setter-based DI, it is a good rule of thumb to use

constructors for mandatory dependencies and setter methods or configuration methods for

optional dependencies. Note that use of the @Required annotation on a setter method can be

used to make the property a required dependency.

The Spring team generally advocates constructor injection as it enables one to implement

application components as immutable objects and to ensure that required dependencies are not

null. Furthermore constructor-injected components are always returned to client (calling) code

in a fully initialized state. As a side note, a large number of constructor arguments is a bad code

smell, implying that the class likely has too many responsibilities and should be refactored to better

address proper separation of concerns.

Setter injection should primarily only be used for optional dependencies that can be assigned

reasonable default values within the class. Otherwise, not-null checks must be performed

everywhere the code uses the dependency. One benefit of setter injection is that setter methods

make objects of that class amenable to reconfiguration or re-injection later. Management through

JMX MBeans is therefore a compelling use case for setter injection.

Use the DI style that makes the most sense for a particular class. Sometimes, when dealing with

third-party classes for which you do not have the source, the choice is made for you. For example,

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 39

if a third-party class does not expose any setter methods, then constructor injection may be the

only available form of DI.

Dependency resolution process

The container performs bean dependency resolution as follows:

• The ApplicationContext is created and initialized with configuration metadata that describes all

the beans. Configuration metadata can be specified via XML, Java code, or annotations.

• For each bean, its dependencies are expressed in the form of properties, constructor arguments, or

arguments to the static-factory method if you are using that instead of a normal constructor. These

dependencies are provided to the bean, when the bean is actually created.

• Each property or constructor argument is an actual definition of the value to set, or a reference to

another bean in the container.

• Each property or constructor argument which is a value is converted from its specified format to the

actual type of that property or constructor argument. By default Spring can convert a value supplied

in string format to all built-in types, such as int, long, String, boolean, etc.

The Spring container validates the configuration of each bean as the container is created. However,

the bean properties themselves are not set until the bean is actually created. Beans that are singleton-

scoped and set to be pre-instantiated (the default) are created when the container is created. Scopes

are defined in Section 5.5, “Bean scopes”. Otherwise, the bean is created only when it is requested.

Creation of a bean potentially causes a graph of beans to be created, as the bean’s dependencies and

its dependencies' dependencies (and so on) are created and assigned. Note that resolution mismatches

among those dependencies may show up late, i.e. on first creation of the affected bean.

Circular dependencies

If you use predominantly constructor injection, it is possible to create an unresolvable circular

dependency scenario.

For example: Class A requires an instance of class B through constructor injection, and class B

requires an instance of class A through constructor injection. If you configure beans for classes

A and B to be injected into each other, the Spring IoC container detects this circular reference at

runtime, and throws a BeanCurrentlyInCreationException.

One possible solution is to edit the source code of some classes to be configured by setters

rather than constructors. Alternatively, avoid constructor injection and use setter injection only. In

other words, although it is not recommended, you can configure circular dependencies with setter

injection.

Unlike the typical case (with no circular dependencies), a circular dependency between bean A

and bean B forces one of the beans to be injected into the other prior to being fully initialized itself

(a classic chicken/egg scenario).

You can generally trust Spring to do the right thing. It detects configuration problems, such as references

to non-existent beans and circular dependencies, at container load-time. Spring sets properties and

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 40

resolves dependencies as late as possible, when the bean is actually created. This means that a Spring

container which has loaded correctly can later generate an exception when you request an object if there

is a problem creating that object or one of its dependencies. For example, the bean throws an exception

as a result of a missing or invalid property. This potentially delayed visibility of some configuration issues

is why ApplicationContext implementations by default pre-instantiate singleton beans. At the cost

of some upfront time and memory to create these beans before they are actually needed, you discover

configuration issues when the ApplicationContext is created, not later. You can still override this

default behavior so that singleton beans will lazy-initialize, rather than be pre-instantiated.

If no circular dependencies exist, when one or more collaborating beans are being injected into a

dependent bean, each collaborating bean is totally configured prior to being injected into the dependent

bean. This means that if bean A has a dependency on bean B, the Spring IoC container completely

configures bean B prior to invoking the setter method on bean A. In other words, the bean is instantiated

(if not a pre-instantiated singleton), its dependencies are set, and the relevant lifecycle methods (such

as a configured init method or the InitializingBean callback method) are invoked.

Examples of dependency injection

The following example uses XML-based configuration metadata for setter-based DI. A small part of a

Spring XML configuration file specifies some bean definitions:

</property>

</bean>

public class ExampleBean {

private AnotherBean beanOne;

private YetAnotherBean beanTwo;

private int i;

public void setBeanOne(AnotherBean beanOne) {

this.beanOne = beanOne;

}

public void setBeanTwo(YetAnotherBean beanTwo) {

this.beanTwo = beanTwo;

}

public void setIntegerProperty(int i) {

this.i = i;

}

In the preceding example, setters are declared to match against the properties specified in the XML file.

The following example uses constructor-based DI:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 41

<constructor-arg>

</constructor-arg>

<constructor-arg ref="yetAnotherBean"/>

<constructor-arg type="int" value="1"/>

</bean>

public class ExampleBean {

private AnotherBean beanOne;

private YetAnotherBean beanTwo;

private int i;

public ExampleBean(

AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {

this.beanOne = anotherBean;

this.beanTwo = yetAnotherBean;

this.i = i;

}

The constructor arguments specified in the bean definition will be used as arguments to the constructor

of the ExampleBean.

Now consider a variant of this example, where instead of using a constructor, Spring is told to call a

static factory method to return an instance of the object:

<constructor-arg ref="anotherExampleBean"/>

<constructor-arg ref="yetAnotherBean"/>

<constructor-arg value="1"/>

</bean>

public class ExampleBean {

// a private constructor

private ExampleBean(...) {

...

}

// a static factory method; the arguments to this method can be

// considered the dependencies of the bean that is returned,

// regardless of how those arguments are actually used.

public static ExampleBean createInstance (

AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {

ExampleBean eb = new ExampleBean (...);

// some other operations...

return eb;

}

Arguments to the static factory method are supplied via <constructor-arg/> elements, exactly

the same as if a constructor had actually been used. The type of the class being returned by the factory

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 42

method does not have to be of the same type as the class that contains the static factory method,

although in this example it is. An instance (non-static) factory method would be used in an essentially

identical fashion (aside from the use of the factory-bean attribute instead of the class attribute),

so details will not be discussed here.

Dependencies and configuration in detail

As mentioned in the previous section, you can define bean properties and constructor arguments as

references to other managed beans (collaborators), or as values defined inline. Spring’s XML-based

configuration metadata supports sub-element types within its <property/> and <constructor-

arg/> elements for this purpose.

Straight values (primitives, Strings, and so on)

The value attribute of the <property/> element specifies a property or constructor argument as a

human-readable string representation. Spring’s conversion service is used to convert these values from

a String to the actual type of the property or argument.

</bean>

The following example uses the p-namespace for even more succinct XML configuration.

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource"

destroy-method="close"

p:driverClassName="com.mysql.jdbc.Driver"

p:url="jdbc:mysql://localhost:3306/mydb"

p:username="root"

p:password="masterkaoli"/>

</beans>

The preceding XML is more succinct; however, typos are discovered at runtime rather than design time,

unless you use an IDE such as IntelliJ IDEA or the Spring Tool Suite (STS) that support automatic

property completion when you create bean definitions. Such IDE assistance is highly recommended.

You can also configure a java.util.Properties instance as:

<bean id="mappings"

class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">

<value>

jdbc.driver.className=com.mysql.jdbc.Driver

jdbc.url=jdbc:mysql://localhost:3306/mydb

</value>

</property>

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 43

The Spring container converts the text inside the <value/> element into a java.util.Properties

instance by using the JavaBeans PropertyEditor mechanism. This is a nice shortcut, and is one of

a few places where the Spring team do favor the use of the nested <value/> element over the value

attribute style.

The idref element

The idref element is simply an error-proof way to pass the id (string value - not a reference) of another

bean in the container to a <constructor-arg/> or <property/> element.

</property>

</bean>

The above bean definition snippet is exactly equivalent (at runtime) to the following snippet:

</bean>

The first form is preferable to the second, because using the idref tag allows the container to validate at

deployment time that the referenced, named bean actually exists. In the second variation, no validation

is performed on the value that is passed to the targetName property of the client bean. Typos are

only discovered (with most likely fatal results) when the client bean is actually instantiated. If the

client bean is a prototype bean, this typo and the resulting exception may only be discovered long

after the container is deployed.

Note

The local attribute on the idref element is no longer supported in the 4.0 beans xsd since

it does not provide value over a regular bean reference anymore. Simply change your existing

idref local references to idref bean when upgrading to the 4.0 schema.

A common place (at least in versions earlier than Spring 2.0) where the <idref/> element brings value

is in the configuration of AOP interceptors in a ProxyFactoryBean bean definition. Using <idref/>

elements when you specify the interceptor names prevents you from misspelling an interceptor id.

References to other beans (collaborators)

The ref element is the final element inside a <constructor-arg/> or <property/> definition

element. Here you set the value of the specified property of a bean to be a reference to another

bean (a collaborator) managed by the container. The referenced bean is a dependency of the bean

whose property will be set, and it is initialized on demand as needed before the property is set. (If

the collaborator is a singleton bean, it may be initialized already by the container.) All references are

ultimately a reference to another object. Scoping and validation depend on whether you specify the id/

name of the other object through the bean, local, or parent attributes.

Specifying the target bean through the bean attribute of the <ref/> tag is the most general form, and

allows creation of a reference to any bean in the same container or parent container, regardless of

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 44

whether it is in the same XML file. The value of the bean attribute may be the same as the id attribute

of the target bean, or as one of the values in the name attribute of the target bean.

Specifying the target bean through the parent attribute creates a reference to a bean that is in a parent

container of the current container. The value of the parent attribute may be the same as either the id

attribute of the target bean, or one of the values in the name attribute of the target bean, and the target

bean must be in a parent container of the current one. You use this bean reference variant mainly when

you have a hierarchy of containers and you want to wrap an existing bean in a parent container with a

proxy that will have the same name as the parent bean.

</bean>

class="org.springframework.aop.framework.ProxyFactoryBean">

</property>

</bean>

Note

The local attribute on the ref element is no longer supported in the 4.0 beans xsd since it

does not provide value over a regular bean reference anymore. Simply change your existing ref

local references to ref bean when upgrading to the 4.0 schema.

Inner beans

A <bean/> element inside the <property/> or <constructor-arg/> elements defines a so-called

inner bean.

</bean>

</property>

</bean>

An inner bean definition does not require a defined id or name; the container ignores these values. It also

ignores the scope flag. Inner beans are always anonymous and they are always created with the outer

bean. It is not possible to inject inner beans into collaborating beans other than into the enclosing bean.

Collections

In the <list/>, <set/>, <map/>, and <props/> elements, you set the properties and arguments of

the Java Collection types List, Set, Map, and Properties, respectively.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 45

<props>

<prop key="administrator">administrator@example.org</prop>

<prop key="support">support@example.org</prop>

<prop key="development">development@example.org</prop>

</props>

</property>

<list>

<value>a list element followed by a reference</value>

</list>

</property>

<map>

</map>

</property>

<set>

<value>just some string</value>

</set>

</property>

</bean>

The value of a map key or value, or a set value, can also again be any of the following elements:

Collection merging

The Spring container also supports the merging of collections. An application developer can define a

parent-style <list/>, <map/>, <set/> or <props/> element, and have child-style <list/>, <map/

>, <set/> or <props/> elements inherit and override values from the parent collection. That is, the

child collection’s values are the result of merging the elements of the parent and child collections, with

the child’s collection elements overriding values specified in the parent collection.

This section on merging discusses the parent-child bean mechanism. Readers unfamiliar with parent

and child bean definitions may wish to read the relevant section before continuing.

The following example demonstrates collection merging:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 46

<beans>

<props>

<prop key="administrator">administrator@example.com</prop>

<prop key="support">support@example.com</prop>

</props>

</property>

</bean>

<prop key="sales">sales@example.com</prop>

<prop key="support">support@example.co.uk</prop>

</props>

</property>

</bean>

<beans>

Notice the use of the merge=true attribute on the <props/> element of the adminEmails property

of the child bean definition. When the child bean is resolved and instantiated by the container, the

resulting instance has an adminEmails Properties collection that contains the result of the merging

of the child’s adminEmails collection with the parent’s adminEmails collection.

administrator=administrator@example.com

sales=sales@example.com

support=support@example.co.uk

The child Properties collection’s value set inherits all property elements from the parent <props/>,

and the child’s value for the support value overrides the value in the parent collection.

This merging behavior applies similarly to the <list/>, <map/>, and <set/> collection types. In the

specific case of the <list/> element, the semantics associated with the List collection type, that is,

the notion of an ordered collection of values, is maintained; the parent’s values precede all of the child

list’s values. In the case of the Map, Set, and Properties collection types, no ordering exists. Hence

no ordering semantics are in effect for the collection types that underlie the associated Map, Set, and

Properties implementation types that the container uses internally.

Limitations of collection merging

You cannot merge different collection types (such as a Map and a List), and if you do attempt to do

so an appropriate Exception is thrown. The merge attribute must be specified on the lower, inherited,

child definition; specifying the merge attribute on a parent collection definition is redundant and will not

result in the desired merging.

Strongly-typed collection

With the introduction of generic types in Java 5, you can use strongly typed collections. That is, it is

possible to declare a Collection type such that it can only contain String elements (for example).

If you are using Spring to dependency-inject a strongly-typed Collection into a bean, you can

take advantage of Spring’s type-conversion support such that the elements of your strongly-typed

Collection instances are converted to the appropriate type prior to being added to the Collection.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 47

public class Foo {

private Map<String, Float> accounts;

public void setAccounts(Map<String, Float> accounts) {

this.accounts = accounts;

}

<beans>

<map>

</map>

</property>

</bean>

</beans>

When the accounts property of the foo bean is prepared for injection, the generics information about

the element type of the strongly-typed Map<String, Float> is available by reflection. Thus Spring’s

type conversion infrastructure recognizes the various value elements as being of type Float, and the

string values 9.99, 2.75, and 3.99 are converted into an actual Float type.

Null and empty string values

Spring treats empty arguments for properties and the like as empty Strings. The following XML-based

configuration metadata snippet sets the email property to the empty String value ("").

</bean>

The preceding example is equivalent to the following Java code:

exampleBean.setEmail("")

The <null/> element handles null values. For example:

<null/>

</property>

</bean>

The above configuration is equivalent to the following Java code:

exampleBean.setEmail(null)

XML shortcut with the p-namespace

The p-namespace enables you to use the bean element’s attributes, instead of nested <property/>

elements, to describe your property values and/or collaborating beans.

Spring supports extensible configuration formats with namespaces, which are based on an XML Schema

definition. The beans configuration format discussed in this chapter is defined in an XML Schema

document. However, the p-namespace is not defined in an XSD file and exists only in the core of Spring.

The following example shows two XML snippets that resolve to the same result: The first uses standard

XML format and the second uses the p-namespace.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 48

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

</bean>

<bean name="p-namespace" class="com.example.ExampleBean"

p:email="foo@bar.com"/>

</beans>

The example shows an attribute in the p-namespace called email in the bean definition. This tells Spring

to include a property declaration. As previously mentioned, the p-namespace does not have a schema

definition, so you can set the name of the attribute to the property name.

This next example includes two more bean definitions that both have a reference to another bean:

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

</bean>

<bean name="john-modern"

class="com.example.Person"

p:name="John Doe"

p:spouse-ref="jane"/>

</bean>

</beans>

As you can see, this example includes not only a property value using the p-namespace, but also uses

a special format to declare property references. Whereas the first bean definition uses <property

name="spouse" ref="jane"/> to create a reference from bean john to bean jane, the second

bean definition uses p:spouse-ref="jane" as an attribute to do the exact same thing. In this case

spouse is the property name, whereas the -ref part indicates that this is not a straight value but rather

a reference to another bean.

Note

The p-namespace is not as flexible as the standard XML format. For example, the format for

declaring property references clashes with properties that end in Ref, whereas the standard XML

format does not. We recommend that you choose your approach carefully and communicate this

to your team members, to avoid producing XML documents that use all three approaches at the

same time.

XML shortcut with the c-namespace

Similar to the the section called “XML shortcut with the p-namespace”, the c-namespace, newly

introduced in Spring 3.1, allows usage of inlined attributes for configuring the constructor arguments

rather then nested constructor-arg elements.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 49

Let’s review the examples from the section called “Constructor-based dependency injection” with the

c: namespace:

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:c="http://www.springframework.org/schema/c"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

<constructor-arg ref="bar"/>

<constructor-arg ref="baz"/>

<constructor-arg value="foo@bar.com"/>

</bean>

</beans>

The c: namespace uses the same conventions as the p: one (trailing -ref for bean references) for

setting the constructor arguments by their names. And just as well, it needs to be declared even though

it is not defined in an XSD schema (but it exists inside the Spring core).

For the rare cases where the constructor argument names are not available (usually if the bytecode was

compiled without debugging information), one can use fallback to the argument indexes:

Note

Due to the XML grammar, the index notation requires the presence of the leading _ as XML

attribute names cannot start with a number (even though some IDE allow it).

In practice, the constructor resolution mechanism is quite efficient in matching arguments so unless one

really needs to, we recommend using the name notation through-out your configuration.

Compound property names

You can use compound or nested property names when you set bean properties, as long as all

components of the path except the final property name are not null. Consider the following bean

definition.

</bean>

The foo bean has a fred property, which has a bob property, which has a sammy property, and that final

sammy property is being set to the value 123. In order for this to work, the fred property of foo, and the

bob property of fred must not be null after the bean is constructed, or a NullPointerException

is thrown.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 50

Using depends-on

If a bean is a dependency of another that usually means that one bean is set as a property of another.

Typically you accomplish this with the <ref/> element in XML-based configuration metadata. However,

sometimes dependencies between beans are less direct; for example, a static initializer in a class needs

to be triggered, such as database driver registration. The depends-on attribute can explicitly force one

or more beans to be initialized before the bean using this element is initialized. The following example

uses the depends-on attribute to express a dependency on a single bean:

To express a dependency on multiple beans, supply a list of bean names as the value of the depends-

on attribute, with commas, whitespace and semicolons, used as valid delimiters:

</bean>

Note

The depends-on attribute in the bean definition can specify both an initialization time dependency

and, in the case of singleton beans only, a corresponding destroy time dependency. Dependent

beans that define a depends-on relationship with a given bean are destroyed first, prior to the

given bean itself being destroyed. Thus depends-on can also control shutdown order.

Lazy-initialized beans

By default, ApplicationContext implementations eagerly create and configure all singleton beans

as part of the initialization process. Generally, this pre-instantiation is desirable, because errors in the

configuration or surrounding environment are discovered immediately, as opposed to hours or even

days later. When this behavior is not desirable, you can prevent pre-instantiation of a singleton bean by

marking the bean definition as lazy-initialized. A lazy-initialized bean tells the IoC container to create a

bean instance when it is first requested, rather than at startup.

In XML, this behavior is controlled by the lazy-init attribute on the <bean/> element; for example:

When the preceding configuration is consumed by an ApplicationContext, the bean named lazy

is not eagerly pre-instantiated when the ApplicationContext is starting up, whereas the not.lazy

bean is eagerly pre-instantiated.

However, when a lazy-initialized bean is a dependency of a singleton bean that is not lazy-initialized,

the ApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the

singleton’s dependencies. The lazy-initialized bean is injected into a singleton bean elsewhere that is

not lazy-initialized.

You can also control lazy-initialization at the container level by using the default-lazy-init attribute

on the <beans/> element; for example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 51

</beans>

Autowiring collaborators

The Spring container can autowire relationships between collaborating beans. You can allow Spring

to resolve collaborators (other beans) automatically for your bean by inspecting the contents of the

ApplicationContext. Autowiring has the following advantages:

• Autowiring can significantly reduce the need to specify properties or constructor arguments. (Other

mechanisms such as a bean template discussed elsewhere in this chapter are also valuable in this

regard.)

• Autowiring can update a configuration as your objects evolve. For example, if you need to add a

dependency to a class, that dependency can be satisfied automatically without you needing to modify

the configuration. Thus autowiring can be especially useful during development, without negating the

option of switching to explicit wiring when the code base becomes more stable.

When using XML-based configuration metadata 10, you specify autowire mode for a bean definition

with the autowire attribute of the <bean/> element. The autowiring functionality has five modes. You

specify autowiring per bean and thus can choose which ones to autowire.

Table 5.2. Autowiring modes

Mode Explanation

no (Default) No autowiring. Bean references must

be defined via a ref element. Changing the

default setting is not recommended for larger

deployments, because specifying collaborators

explicitly gives greater control and clarity. To

some extent, it documents the structure of a

system.

byName Autowiring by property name. Spring looks for

a bean with the same name as the property

that needs to be autowired. For example, if a

bean definition is set to autowire by name, and

it contains a master property (that is, it has a

setMaster(..) method), Spring looks for a bean

definition named master, and uses it to set the

property.

byType Allows a property to be autowired if exactly one

bean of the property type exists in the container.

If more than one exists, a fatal exception is

thrown, which indicates that you may not use

byType autowiring for that bean. If there are no

matching beans, nothing happens; the property

is not set.

10See the section called “Dependency injection”

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 52

Mode Explanation

constructor Analogous to byType, but applies to constructor

arguments. If there is not exactly one bean of

the constructor argument type in the container, a

fatal error is raised.

With byType or constructor autowiring mode, you can wire arrays and typed-collections. In such cases

all autowire candidates within the container that match the expected type are provided to satisfy the

dependency. You can autowire strongly-typed Maps if the expected key type is String. An autowired

Maps values will consist of all bean instances that match the expected type, and the Maps keys will

contain the corresponding bean names.

You can combine autowire behavior with dependency checking, which is performed after autowiring

completes.

Limitations and disadvantages of autowiring

Autowiring works best when it is used consistently across a project. If autowiring is not used in general,

it might be confusing to developers to use it to wire only one or two bean definitions.

Consider the limitations and disadvantages of autowiring:

• Explicit dependencies in property and constructor-arg settings always override autowiring.

You cannot autowire so-called simple properties such as primitives, Strings, and Classes (and

arrays of such simple properties). This limitation is by-design.

• Autowiring is less exact than explicit wiring. Although, as noted in the above table, Spring is careful

to avoid guessing in case of ambiguity that might have unexpected results, the relationships between

your Spring-managed objects are no longer documented explicitly.

• Wiring information may not be available to tools that may generate documentation from a Spring

container.

• Multiple bean definitions within the container may match the type specified by the setter method

or constructor argument to be autowired. For arrays, collections, or Maps, this is not necessarily

a problem. However for dependencies that expect a single value, this ambiguity is not arbitrarily

resolved. If no unique bean definition is available, an exception is thrown.

In the latter scenario, you have several options:

• Abandon autowiring in favor of explicit wiring.

• Avoid autowiring for a bean definition by setting its autowire-candidate attributes to false as

described in the next section.

• Designate a single bean definition as the primary candidate by setting the primary attribute of its

<bean/> element to true.

• Implement the more fine-grained control available with annotation-based configuration, as described

in Section 5.9, “Annotation-based container configuration”.

Excluding a bean from autowiring

On a per-bean basis, you can exclude a bean from autowiring. In Spring’s XML format, set the

autowire-candidate attribute of the <bean/> element to false; the container makes that specific

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 53

bean definition unavailable to the autowiring infrastructure (including annotation style configurations

such as @Autowired).

You can also limit autowire candidates based on pattern-matching against bean names. The top-

level <beans/> element accepts one or more patterns within its default-autowire-candidates

attribute. For example, to limit autowire candidate status to any bean whose name ends with Repository,

provide a value of *Repository. To provide multiple patterns, define them in a comma-separated list. An

explicit value of true or false for a bean definitions autowire-candidate attribute always takes

precedence, and for such beans, the pattern matching rules do not apply.

These techniques are useful for beans that you never want to be injected into other beans by autowiring.

It does not mean that an excluded bean cannot itself be configured using autowiring. Rather, the bean

itself is not a candidate for autowiring other beans.

Method injection

In most application scenarios, most beans in the container are singletons. When a singleton bean needs

to collaborate with another singleton bean, or a non-singleton bean needs to collaborate with another

non-singleton bean, you typically handle the dependency by defining one bean as a property of the

other. A problem arises when the bean lifecycles are different. Suppose singleton bean A needs to use

non-singleton (prototype) bean B, perhaps on each method invocation on A. The container only creates

the singleton bean A once, and thus only gets one opportunity to set the properties. The container cannot

provide bean A with a new instance of bean B every time one is needed.

A solution is to forego some inversion of control. You can make bean A aware of the container by

implementing the ApplicationContextAware interface, and by making a getBean("B") call to the

container ask for (a typically new) bean B instance every time bean A needs it. The following is an

example of this approach:

// a class that uses a stateful Command-style class to perform some processing

package fiona.apple;

// Spring-API imports

import org.springframework.beans.BeansException;

import org.springframework.context.ApplicationContext;

import org.springframework.context.ApplicationContextAware;

public class CommandManager implements ApplicationContextAware {

private ApplicationContext applicationContext;

public Object process(Map commandState) {

// grab a new instance of the appropriate Command

Command command = createCommand();

// set the state on the (hopefully brand new) Command instance

command.setState(commandState);

return command.execute();

}

protected Command createCommand() {

// notice the Spring API dependency!

return this.applicationContext.getBean("command", Command.class);

}

public void setApplicationContext(

ApplicationContext applicationContext) throws BeansException {

this.applicationContext = applicationContext;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 54

The preceding is not desirable, because the business code is aware of and coupled to the Spring

Framework. Method Injection, a somewhat advanced feature of the Spring IoC container, allows this

use case to be handled in a clean fashion.

You can read more about the motivation for Method Injection in this blog entry.

Lookup method injection

Lookup method injection is the ability of the container to override methods on container managed beans,

to return the lookup result for another named bean in the container. The lookup typically involves a

prototype bean as in the scenario described in the preceding section. The Spring Framework implements

this method injection by using bytecode generation from the CGLIB library to generate dynamically a

subclass that overrides the method.

Note

For this dynamic subclassing to work, the class that the Spring container will subclass cannot

be final, and the method to be overridden cannot be final either. Also, testing a class that

has an abstract method requires you to subclass the class yourself and to supply a stub

implementation of the abstract method. Finally, objects that have been the target of method

injection cannot be serialized. As of Spring 3.2 it is no longer necessary to add CGLIB to your

classpath, because CGLIB classes are repackaged under org.springframework and distributed

within the spring-core JAR. This is done both for convenience as well as to avoid potential conflicts

with other projects that use differing versions of CGLIB.

Looking at the CommandManager class in the previous code snippet, you see that the Spring

container will dynamically override the implementation of the createCommand() method. Your

CommandManager class will not have any Spring dependencies, as can be seen in the reworked

example:

package fiona.apple;

// no more Spring imports!

public abstract class CommandManager {

public Object process(Object commandState) {

// grab a new instance of the appropriate Command interface

Command command = createCommand();

// set the state on the (hopefully brand new) Command instance

command.setState(commandState);

return command.execute();

}

// okay... but where is the implementation of this method?

protected abstract Command createCommand();

}

In the client class containing the method to be injected (the CommandManager in this case), the method

to be injected requires a signature of the following form:

<public|protected> [abstract] <return-type> theMethodName(no-arguments);

If the method is abstract, the dynamically-generated subclass implements the method. Otherwise,

the dynamically-generated subclass overrides the concrete method defined in the original class. For

example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 55

</bean>

<lookup-method name="createCommand" bean="command"/>

</bean>

The bean identified as commandManager calls its own method createCommand() whenever it needs

a new instance of the command bean. You must be careful to deploy the command bean as a prototype,

if that is actually what is needed. If it is deployed as a singleton, the same instance of the command

bean is returned each time.

Tip

The interested reader may also find the ServiceLocatorFactoryBean (in the

org.springframework.beans.factory.config package) to be of use. The approach

used in ServiceLocatorFactoryBean is similar to that of another utility class,

ObjectFactoryCreatingFactoryBean, but it allows you to specify your own lookup interface

as opposed to a Spring-specific lookup interface. Consult the javadocs of these classes for

additional information.

Arbitrary method replacement

A less useful form of method injection than lookup method Injection is the ability to replace arbitrary

methods in a managed bean with another method implementation. Users may safely skip the rest of

this section until the functionality is actually needed.

With XML-based configuration metadata, you can use the replaced-method element to replace an

existing method implementation with another, for a deployed bean. Consider the following class, with

a method computeValue, which we want to override:

public class MyValueCalculator {

public String computeValue(String input) {

// some real code...

}

// some other methods...

}

A class implementing the org.springframework.beans.factory.support.MethodReplacer

interface provides the new method definition.

/**

* meant to be used to override the existing computeValue(String)

* implementation in MyValueCalculator

public class ReplacementComputeValue implements MethodReplacer {

public Object reimplement(Object o, Method m, Object[] args) throws Throwable {

// get the input value, work with it, and return a computed result

String input = (String) args[0];

...

return ...;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 56

The bean definition to deploy the original class and specify the method override would look like this:

<replaced-method name="computeValue" replacer="replacementComputeValue">

<arg-type>String</arg-type>

</replaced-method>

</bean>

You can use one or more contained <arg-type/> elements within the <replaced-method/>

element to indicate the method signature of the method being overridden. The signature for the

arguments is necessary only if the method is overloaded and multiple variants exist within the class.

For convenience, the type string for an argument may be a substring of the fully qualified type name.

For example, the following all match java.lang.String:

java.lang.String

String

Str

Because the number of arguments is often enough to distinguish between each possible choice, this

shortcut can save a lot of typing, by allowing you to type only the shortest string that will match an

argument type.

5.5 Bean scopes

When you create a bean definition, you create a recipe for creating actual instances of the class defined

by that bean definition. The idea that a bean definition is a recipe is important, because it means that,

as with a class, you can create many object instances from a single recipe.

You can control not only the various dependencies and configuration values that are to be plugged into

an object that is created from a particular bean definition, but also the scope of the objects created from

a particular bean definition. This approach is powerful and flexible in that you can choose the scope

of the objects you create through configuration instead of having to bake in the scope of an object at

the Java class level. Beans can be defined to be deployed in one of a number of scopes: out of the

box, the Spring Framework supports five scopes, three of which are available only if you use a web-

aware ApplicationContext.

The following scopes are supported out of the box. You can also create a custom scope.

Table 5.3. Bean scopes

Scope Description

singleton (Default) Scopes a single bean definition to a

single object instance per Spring IoC container.

prototype Scopes a single bean definition to any number of

object instances.

request Scopes a single bean definition to the lifecycle

of a single HTTP request; that is, each HTTP

request has its own instance of a bean created

off the back of a single bean definition. Only

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 57

Scope Description

valid in the context of a web-aware Spring

ApplicationContext.

session Scopes a single bean definition to the lifecycle of

an HTTP Session. Only valid in the context of a

web-aware Spring ApplicationContext.

global session Scopes a single bean definition to the lifecycle

of a global HTTP Session. Typically only

valid when used in a portlet context. Only

valid in the context of a web-aware Spring

ApplicationContext.

application Scopes a single bean definition to the lifecycle of

a ServletContext. Only valid in the context of

a web-aware Spring ApplicationContext.

Note

As of Spring 3.0, a thread scope is available, but is not registered by default. For more information,

see the documentation for SimpleThreadScope. For instructions on how to register this or any

other custom scope, see the section called “Using a custom scope”.

The singleton scope

Only one shared instance of a singleton bean is managed, and all requests for beans with an id or

ids matching that bean definition result in that one specific bean instance being returned by the Spring

container.

To put it another way, when you define a bean definition and it is scoped as a singleton, the Spring IoC

container creates exactly one instance of the object defined by that bean definition. This single instance

is stored in a cache of such singleton beans, and all subsequent requests and references for that named

bean return the cached object.

Figure 5.2.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 58

Spring’s concept of a singleton bean differs from the Singleton pattern as defined in the Gang of Four

(GoF) patterns book. The GoF Singleton hard-codes the scope of an object such that one and only

one instance of a particular class is created per ClassLoader. The scope of the Spring singleton is best

described as per container and per bean. This means that if you define one bean for a particular class

in a single Spring container, then the Spring container creates one and only one instance of the class

defined by that bean definition. The singleton scope is the default scope in Spring. To define a bean as

a singleton in XML, you would write, for example:

The prototype scope

The non-singleton, prototype scope of bean deployment results in the creation of a new bean instance

every time a request for that specific bean is made. That is, the bean is injected into another bean or

you request it through a getBean() method call on the container. As a rule, use the prototype scope

for all stateful beans and the singleton scope for stateless beans.

The following diagram illustrates the Spring prototype scope. A data access object (DAO) is not typically

configured as a prototype, because a typical DAO does not hold any conversational state; it was just

easier for this author to reuse the core of the singleton diagram.

Figure 5.3.

The following example defines a bean as a prototype in XML:

In contrast to the other scopes, Spring does not manage the complete lifecycle of a prototype bean: the

container instantiates, configures, and otherwise assembles a prototype object, and hands it to the client,

with no further record of that prototype instance. Thus, although initialization lifecycle callback methods

are called on all objects regardless of scope, in the case of prototypes, configured destruction lifecycle

callbacks are not called. The client code must clean up prototype-scoped objects and release expensive

resources that the prototype bean(s) are holding. To get the Spring container to release resources held

by prototype-scoped beans, try using a custom bean post-processor, which holds a reference to beans

that need to be cleaned up.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 59

In some respects, the Spring container’s role in regard to a prototype-scoped bean is a replacement

for the Java new operator. All lifecycle management past that point must be handled by the client. (For

details on the lifecycle of a bean in the Spring container, see the section called “Lifecycle callbacks”.)

Singleton beans with prototype-bean dependencies

When you use singleton-scoped beans with dependencies on prototype beans, be aware that

dependencies are resolved at instantiation time. Thus if you dependency-inject a prototype-scoped bean

into a singleton-scoped bean, a new prototype bean is instantiated and then dependency-injected into

the singleton bean. The prototype instance is the sole instance that is ever supplied to the singleton-

scoped bean.

However, suppose you want the singleton-scoped bean to acquire a new instance of the prototype-

scoped bean repeatedly at runtime. You cannot dependency-inject a prototype-scoped bean into your

singleton bean, because that injection occurs only once, when the Spring container is instantiating the

singleton bean and resolving and injecting its dependencies. If you need a new instance of a prototype

bean at runtime more than once, see the section called “Method injection”

Request, session, and global session scopes

The request, session, and global session scopes are only available if you use a web-aware

Spring ApplicationContext implementation (such as XmlWebApplicationContext). If you use

these scopes with regular Spring IoC containers such as the ClassPathXmlApplicationContext,

you get an IllegalStateException complaining about an unknown bean scope.

Initial web configuration

To support the scoping of beans at the request, session, and global session levels (web-scoped

beans), some minor initial configuration is required before you define your beans. (This initial setup is

not required for the standard scopes, singleton and prototype.)

How you accomplish this initial setup depends on your particular Servlet environment..

If you access scoped beans within Spring Web MVC, in effect, within a request that is processed

by the Spring DispatcherServlet, or DispatcherPortlet, then no special setup is necessary:

DispatcherServlet and DispatcherPortlet already expose all relevant state.

If you use a Servlet 2.5 web container, with requests processed outside of

Spring’s DispatcherServlet (for example, when using JSF or Struts), you need

to register the org.springframework.web.context.request.RequestContextListener

ServletRequestListener. For Servlet 3.0+, this can done programmatically via the

WebApplicationInitializer interface. Alternatively, or for older containers, add the following

declaration to your web application’s web.xml file:

<web-app>

...

<listener-class>

org.springframework.web.context.request.RequestContextListener

</listener-class>

</listener>

...

</web-app>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 60

Alternatively, if there are issues with your listener setup, consider the provided

RequestContextFilter. The filter mapping depends on the surrounding web application

configuration, so you have to change it as appropriate.

<web-app>

...

<filter-name>requestContextFilter</filter-name>

<filter-class>org.springframework.web.filter.RequestContextFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>requestContextFilter</filter-name>

<url-pattern>/*</url-pattern>

</filter-mapping>

...

</web-app>

DispatcherServlet, RequestContextListener and RequestContextFilter all do exactly

the same thing, namely bind the HTTP request object to the Thread that is servicing that request. This

makes beans that are request- and session-scoped available further down the call chain.

Request scope

Consider the following bean definition:

The Spring container creates a new instance of the LoginAction bean by using the loginAction

bean definition for each and every HTTP request. That is, the loginAction bean is scoped at the

HTTP request level. You can change the internal state of the instance that is created as much as you

want, because other instances created from the same loginAction bean definition will not see these

changes in state; they are particular to an individual request. When the request completes processing,

the bean that is scoped to the request is discarded.

Session scope

Consider the following bean definition:

The Spring container creates a new instance of the UserPreferences bean by using the

userPreferences bean definition for the lifetime of a single HTTP Session. In other words, the

userPreferences bean is effectively scoped at the HTTP Session level. As with request-scoped

beans, you can change the internal state of the instance that is created as much as you want,

knowing that other HTTP Session instances that are also using instances created from the same

userPreferences bean definition do not see these changes in state, because they are particular to an

individual HTTP Session. When the HTTP Session is eventually discarded, the bean that is scoped

to that particular HTTP Session is also discarded.

Global session scope

Consider the following bean definition:

The global session scope is similar to the standard HTTP Session scope (described above), and

applies only in the context of portlet-based web applications. The portlet specification defines the notion

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 61

of a global Session that is shared among all portlets that make up a single portlet web application.

Beans defined at the global session scope are scoped (or bound) to the lifetime of the global portlet

Session.

If you write a standard Servlet-based web application and you define one or more beans as having

global session scope, the standard HTTP Session scope is used, and no error is raised.

Application scope

Consider the following bean definition:

The Spring container creates a new instance of the AppPreferences bean by using the

appPreferences bean definition once for the entire web application. That is, the appPreferences

bean is scoped at the ServletContext level, stored as a regular ServletContext attribute. This

is somewhat similar to a Spring singleton bean but differs in two important ways: It is a singleton per

ServletContext, not per Spring ApplicationContext (or which there may be several in any given web

application), and it is actually exposed and therefore visible as a ServletContext attribute.

Scoped beans as dependencies

The Spring IoC container manages not only the instantiation of your objects (beans), but also the wiring

up of collaborators (or dependencies). If you want to inject (for example) an HTTP request scoped bean

into another bean, you must inject an AOP proxy in place of the scoped bean. That is, you need to inject

a proxy object that exposes the same public interface as the scoped object but that can also retrieve

the real, target object from the relevant scope (for example, an HTTP request) and delegate method

calls onto the real object.

Note

You do not need to use the <aop:scoped-proxy/> in conjunction with beans that are scoped

as singletons or prototypes.

The configuration in the following example is only one line, but it is important to understand the "why"

as well as the "how" behind it.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<aop:scoped-proxy/>

</bean>

</bean>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 62

To create such a proxy, you insert a child <aop:scoped-proxy/> element into a scoped bean

definition. See the section called “Choosing the type of proxy to create” and Chapter 34, XML Schema-

based configuration.) Why do definitions of beans scoped at the request, session, globalSession

and custom-scope levels require the <aop:scoped-proxy/> element ? Let’s examine the following

singleton bean definition and contrast it with what you need to define for the aforementioned scopes.

(The following userPreferences bean definition as it stands is incomplete.)

</bean>

In the preceding example, the singleton bean userManager is injected with a reference to the HTTP

Session-scoped bean userPreferences. The salient point here is that the userManager bean is a

singleton: it will be instantiated exactly once per container, and its dependencies (in this case only one,

the userPreferences bean) are also injected only once. This means that the userManager bean

will only operate on the exact same userPreferences object, that is, the one that it was originally

injected with.

This is not the behavior you want when injecting a shorter-lived scoped bean into a longer-

lived scoped bean, for example injecting an HTTP Session-scoped collaborating bean as a

dependency into singleton bean. Rather, you need a single userManager object, and for the

lifetime of an HTTP Session, you need a userPreferences object that is specific to said HTTP

Session. Thus the container creates an object that exposes the exact same public interface as

the UserPreferences class (ideally an object that is a UserPreferences instance) which can

fetch the real UserPreferences object from the scoping mechanism (HTTP request, Session,

etc.). The container injects this proxy object into the userManager bean, which is unaware that this

UserPreferences reference is a proxy. In this example, when a UserManager instance invokes

a method on the dependency-injected UserPreferences object, it actually is invoking a method on

the proxy. The proxy then fetches the real UserPreferences object from (in this case) the HTTP

Session, and delegates the method invocation onto the retrieved real UserPreferences object.

Thus you need the following, correct and complete, configuration when injecting request-, session-,

and globalSession-scoped beans into collaborating objects:

<aop:scoped-proxy/>

</bean>

</bean>

Choosing the type of proxy to create

By default, when the Spring container creates a proxy for a bean that is marked up with the

<aop:scoped-proxy/> element, a CGLIB-based class proxy is created.

Note

CGLIB proxies only intercept public method calls! Do not call non-public methods on such a proxy;

they will not be delegated to the actual scoped target object.

Alternatively, you can configure the Spring container to create standard JDK interface-based proxies

for such scoped beans, by specifying false for the value of the proxy-target-class attribute of

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 63

the <aop:scoped-proxy/> element. Using JDK interface-based proxies means that you do not need

additional libraries in your application classpath to effect such proxying. However, it also means that the

class of the scoped bean must implement at least one interface, and that all collaborators into which the

scoped bean is injected must reference the bean through one of its interfaces.

<aop:scoped-proxy proxy-target-class="false"/>

</bean>

</bean>

For more detailed information about choosing class-based or interface-based proxying, see Section 9.6,

“Proxying mechanisms”.

Custom scopes

The bean scoping mechanism is extensible; You can define your own scopes, or even redefine existing

scopes, although the latter is considered bad practice and you cannot override the built-in singleton

and prototype scopes.

Creating a custom scope

To integrate your custom scope(s) into the Spring container, you need to implement the

org.springframework.beans.factory.config.Scope interface, which is described in this

section. For an idea of how to implement your own scopes, see the Scope implementations that are

supplied with the Spring Framework itself and the Scope javadocs, which explains the methods you

need to implement in more detail.

The Scope interface has four methods to get objects from the scope, remove them from the scope,

and allow them to be destroyed.

The following method returns the object from the underlying scope. The session scope implementation,

for example, returns the session-scoped bean (and if it does not exist, the method returns a new instance

of the bean, after having bound it to the session for future reference).

Object get(String name, ObjectFactory objectFactory)

The following method removes the object from the underlying scope. The session scope implementation

for example, removes the session-scoped bean from the underlying session. The object should be

returned, but you can return null if the object with the specified name is not found.

Object remove(String name)

The following method registers the callbacks the scope should execute when it is destroyed or when

the specified object in the scope is destroyed. Refer to the javadocs or a Spring scope implementation

for more information on destruction callbacks.

void registerDestructionCallback(String name, Runnable destructionCallback)

The following method obtains the conversation identifier for the underlying scope. This identifier is

different for each scope. For a session scoped implementation, this identifier can be the session

identifier.

String getConversationId()

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 64

Using a custom scope

After you write and test one or more custom Scope implementations, you need to make the Spring

container aware of your new scope(s). The following method is the central method to register a new

Scope with the Spring container:

void registerScope(String scopeName, Scope scope);

This method is declared on the ConfigurableBeanFactory interface, which is available on most

of the concrete ApplicationContext implementations that ship with Spring via the BeanFactory

property.

The first argument to the registerScope(..) method is the unique name associated with a

scope; examples of such names in the Spring container itself are singleton and prototype. The

second argument to the registerScope(..) method is an actual instance of the custom Scope

implementation that you wish to register and use.

Suppose that you write your custom Scope implementation, and then register it as below.

Note

The example below uses SimpleThreadScope which is included with Spring, but not registered

by default. The instructions would be the same for your own custom Scope implementations.

Scope threadScope = new SimpleThreadScope();

beanFactory.registerScope("thread", threadScope);

You then create bean definitions that adhere to the scoping rules of your custom Scope:

With a custom Scope implementation, you are not limited to programmatic registration of the scope.

You can also do the Scope registration declaratively, using the CustomScopeConfigurer class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 65

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<map>

</entry>

</map>

</property>

</bean>

<aop:scoped-proxy/>

</bean>

</bean>

</beans>

Note

When you place <aop:scoped-proxy/> in a FactoryBean implementation, it is the factory

bean itself that is scoped, not the object returned from getObject().

5.6 Customizing the nature of a bean

Lifecycle callbacks

To interact with the container’s management of the bean lifecycle, you can implement

the Spring InitializingBean and DisposableBean interfaces. The container calls

afterPropertiesSet() for the former and destroy() for the latter to allow the bean to perform

certain actions upon initialization and destruction of your beans.

Tip

The JSR-250 @PostConstruct and @PreDestroy annotations are generally considered best

practice for receiving lifecycle callbacks in a modern Spring application. Using these annotations

means that your beans are not coupled to Spring specific interfaces. For details see the section

called “@PostConstruct and @PreDestroy”.

If you don’t want to use the JSR-250 annotations but you are still looking to remove coupling

consider the use of init-method and destroy-method object definition metadata.

Internally, the Spring Framework uses BeanPostProcessor implementations to process any callback

interfaces it can find and call the appropriate methods. If you need custom features or other lifecycle

behavior Spring does not offer out-of-the-box, you can implement a BeanPostProcessor yourself.

For more information, see Section 5.8, “Container Extension Points”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 66

In addition to the initialization and destruction callbacks, Spring-managed objects may also implement

the Lifecycle interface so that those objects can participate in the startup and shutdown process as

driven by the container’s own lifecycle.

The lifecycle callback interfaces are described in this section.

Initialization callbacks

The org.springframework.beans.factory.InitializingBean interface allows a bean to

perform initialization work after all necessary properties on the bean have been set by the container.

The InitializingBean interface specifies a single method:

void afterPropertiesSet() throws Exception;

It is recommended that you do not use the InitializingBean interface because it unnecessarily

couples the code to Spring. Alternatively, use the @PostConstruct annotation or specify a POJO

initialization method. In the case of XML-based configuration metadata, you use the init-method

attribute to specify the name of the method that has a void no-argument signature. For example, the

following definition:

public class ExampleBean {

public void init() {

// do some initialization work

}

…is exactly the same as…

public class AnotherExampleBean implements InitializingBean {

public void afterPropertiesSet() {

// do some initialization work

}

but does not couple the code to Spring.

Destruction callbacks

Implementing the org.springframework.beans.factory.DisposableBean interface allows a

bean to get a callback when the container containing it is destroyed. The DisposableBean interface

specifies a single method:

void destroy() throws Exception;

It is recommended that you do not use the DisposableBean callback interface because it

unnecessarily couples the code to Spring. Alternatively, use the @PreDestroy annotation or specify

a generic method that is supported by bean definitions. With XML-based configuration metadata, you

use the destroy-method attribute on the <bean/>. For example, the following definition:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 67

public class ExampleBean {

public void cleanup() {

// do some destruction work (like releasing pooled connections)

}

is exactly the same as:

public class AnotherExampleBean implements DisposableBean {

public void destroy() {

// do some destruction work (like releasing pooled connections)

}

but does not couple the code to Spring.

Default initialization and destroy methods

When you write initialization and destroy method callbacks that do not use the Spring-specific

InitializingBean and DisposableBean callback interfaces, you typically write methods with

names such as init(), initialize(), dispose(), and so on. Ideally, the names of such lifecycle

callback methods are standardized across a project so that all developers use the same method names

and ensure consistency.

You can configure the Spring container to look for named initialization and destroy callback method

names on every bean. This means that you, as an application developer, can write your application

classes and use an initialization callback called init(), without having to configure an init-

method="init" attribute with each bean definition. The Spring IoC container calls that method

when the bean is created (and in accordance with the standard lifecycle callback contract described

previously). This feature also enforces a consistent naming convention for initialization and destroy

method callbacks.

Suppose that your initialization callback methods are named init() and destroy callback methods are

named destroy(). Your class will resemble the class in the following example.

public class DefaultBlogService implements BlogService {

private BlogDao blogDao;

public void setBlogDao(BlogDao blogDao) {

this.blogDao = blogDao;

}

// this is (unsurprisingly) the initialization callback method

public void init() {

if (this.blogDao == null) {

throw new IllegalStateException("The [blogDao] property must be set.");

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 68

</bean>

</beans>

The presence of the default-init-method attribute on the top-level <beans/> element attribute

causes the Spring IoC container to recognize a method called init on beans as the initialization method

callback. When a bean is created and assembled, if the bean class has such a method, it is invoked

at the appropriate time.

You configure destroy method callbacks similarly (in XML, that is) by using the default-destroy-

method attribute on the top-level <beans/> element.

Where existing bean classes already have callback methods that are named at variance with the

convention, you can override the default by specifying (in XML, that is) the method name using the

init-method and destroy-method attributes of the <bean/> itself.

The Spring container guarantees that a configured initialization callback is called immediately after

a bean is supplied with all dependencies. Thus the initialization callback is called on the raw bean

reference, which means that AOP interceptors and so forth are not yet applied to the bean. A target

bean is fully created first, then an AOP proxy (for example) with its interceptor chain is applied. If the

target bean and the proxy are defined separately, your code can even interact with the raw target bean,

bypassing the proxy. Hence, it would be inconsistent to apply the interceptors to the init method, because

doing so would couple the lifecycle of the target bean with its proxy/interceptors and leave strange

semantics when your code interacts directly to the raw target bean.

Combining lifecycle mechanisms

As of Spring 2.5, you have three options for controlling bean lifecycle behavior: the InitializingBean

and DisposableBean callback interfaces; custom init() and destroy() methods; and the

@PostConstruct and @PreDestroy annotations. You can combine these mechanisms to control a

given bean.

Note

If multiple lifecycle mechanisms are configured for a bean, and each mechanism is configured

with a different method name, then each configured method is executed in the order listed below.

However, if the same method name is configured - for example, init() for an initialization

method - for more than one of these lifecycle mechanisms, that method is executed once, as

explained in the preceding section.

Multiple lifecycle mechanisms configured for the same bean, with different initialization methods, are

called as follows:

• Methods annotated with @PostConstruct

•afterPropertiesSet() as defined by the InitializingBean callback interface

• A custom configured init() method

Destroy methods are called in the same order:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 69

• Methods annotated with @PreDestroy

•destroy() as defined by the DisposableBean callback interface

• A custom configured destroy() method

Startup and shutdown callbacks

The Lifecycle interface defines the essential methods for any object that has its own lifecycle

requirements (e.g. starts and stops some background process):

public interface Lifecycle {

void start();

void stop();

boolean isRunning();

}

Any Spring-managed object may implement that interface. Then, when the ApplicationContext

itself starts and stops, it will cascade those calls to all Lifecycle implementations defined within that

context. It does this by delegating to a LifecycleProcessor:

public interface LifecycleProcessor extends Lifecycle {

void onRefresh();

void onClose();

}

Notice that the LifecycleProcessor is itself an extension of the Lifecycle interface. It also adds

two other methods for reacting to the context being refreshed and closed.

The order of startup and shutdown invocations can be important. If a "depends-on" relationship exists

between any two objects, the dependent side will start after its dependency, and it will stop before its

dependency. However, at times the direct dependencies are unknown. You may only know that objects

of a certain type should start prior to objects of another type. In those cases, the SmartLifecycle

interface defines another option, namely the getPhase() method as defined on its super-interface,

Phased.

public interface Phased {

int getPhase();

}

public interface SmartLifecycle extends Lifecycle, Phased {

boolean isAutoStartup();

void stop(Runnable callback);

}

When starting, the objects with the lowest phase start first, and when stopping, the reverse order is

followed. Therefore, an object that implements SmartLifecycle and whose getPhase() method

returns Integer.MIN_VALUE would be among the first to start and the last to stop. At the other end of

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 70

the spectrum, a phase value of Integer.MAX_VALUE would indicate that the object should be started

last and stopped first (likely because it depends on other processes to be running). When considering

the phase value, it’s also important to know that the default phase for any "normal" Lifecycle object

that does not implement SmartLifecycle would be 0. Therefore, any negative phase value would

indicate that an object should start before those standard components (and stop after them), and vice

versa for any positive phase value.

As you can see the stop method defined by SmartLifecycle accepts a callback. Any implementation

must invoke that callback’s run() method after that implementation’s shutdown process is complete.

That enables asynchronous shutdown where necessary since the default implementation of the

LifecycleProcessor interface, DefaultLifecycleProcessor, will wait up to its timeout value

for the group of objects within each phase to invoke that callback. The default per-phase timeout

is 30 seconds. You can override the default lifecycle processor instance by defining a bean named

"lifecycleProcessor" within the context. If you only want to modify the timeout, then defining the following

would be sufficient:

</bean>

As mentioned, the LifecycleProcessor interface defines callback methods for the refreshing and

closing of the context as well. The latter will simply drive the shutdown process as if stop() had

been called explicitly, but it will happen when the context is closing. The refresh callback on the other

hand enables another feature of SmartLifecycle beans. When the context is refreshed (after all

objects have been instantiated and initialized), that callback will be invoked, and at that point the

default lifecycle processor will check the boolean value returned by each SmartLifecycle object’s

isAutoStartup() method. If "true", then that object will be started at that point rather than waiting for

an explicit invocation of the context’s or its own start() method (unlike the context refresh, the context

start does not happen automatically for a standard context implementation). The "phase" value as well

as any "depends-on" relationships will determine the startup order in the same way as described above.

Shutting down the Spring IoC container gracefully in non-web applications

Note

This section applies only to non-web applications. Spring’s web-based ApplicationContext

implementations already have code in place to shut down the Spring IoC container gracefully

when the relevant web application is shut down.

If you are using Spring’s IoC container in a non-web application environment; for example, in a rich

client desktop environment; you register a shutdown hook with the JVM. Doing so ensures a graceful

shutdown and calls the relevant destroy methods on your singleton beans so that all resources are

released. Of course, you must still configure and implement these destroy callbacks correctly.

To register a shutdown hook, you call the registerShutdownHook() method that is declared on the

AbstractApplicationContext class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 71

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public final class Boot {

public static void main(final String[] args) throws Exception {

AbstractApplicationContext ctx = new ClassPathXmlApplicationContext(

new String []{"beans.xml"});

// add a shutdown hook for the above context...

ctx.registerShutdownHook();

// app runs here...

// main method exits, hook is called prior to the app shutting down...

}

ApplicationContextAware and BeanNameAware

When an ApplicationContext creates an object instance that implements the

org.springframework.context.ApplicationContextAware interface, the instance is

provided with a reference to that ApplicationContext.

public interface ApplicationContextAware {

void setApplicationContext(ApplicationContext applicationContext) throws BeansException;

}

Thus beans can manipulate programmatically the ApplicationContext that created them, through

the ApplicationContext interface, or by casting the reference to a known subclass of this interface,

such as ConfigurableApplicationContext, which exposes additional functionality. One use

would be the programmatic retrieval of other beans. Sometimes this capability is useful; however, in

general you should avoid it, because it couples the code to Spring and does not follow the Inversion

of Control style, where collaborators are provided to beans as properties. Other methods of the

ApplicationContext provide access to file resources, publishing application events, and accessing

a MessageSource. These additional features are described in Section 5.15, “Additional Capabilities

of the ApplicationContext”

As of Spring 2.5, autowiring is another alternative to obtain reference to the ApplicationContext.

The "traditional" constructor and byType autowiring modes (as described in the section called

“Autowiring collaborators”) can provide a dependency of type ApplicationContext for a constructor

argument or setter method parameter, respectively. For more flexibility, including the ability to autowire

fields and multiple parameter methods, use the new annotation-based autowiring features. If you do,

the ApplicationContext is autowired into a field, constructor argument, or method parameter that

is expecting the ApplicationContext type if the field, constructor, or method in question carries the

@Autowired annotation. For more information, see the section called “@Autowired”.

When an ApplicationContext creates a class that implements the

org.springframework.beans.factory.BeanNameAware interface, the class is provided with a

reference to the name defined in its associated object definition.

public interface BeanNameAware {

void setBeanName(string name) throws BeansException;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 72

The callback is invoked after population of normal bean properties but before an initialization callback

such as InitializingBean afterPropertiesSet or a custom init-method.

Other Aware interfaces

Besides ApplicationContextAware and BeanNameAware discussed above, Spring offers a range

of Aware interfaces that allow beans to indicate to the container that they require a certain infrastructure

dependency. The most important Aware interfaces are summarized below - as a general rule, the name

is a good indication of the dependency type:

Table 5.4. Aware interfaces

Name Injected Dependency Explained in…

ApplicationContextAware Declaring

ApplicationContext

the section called

“ApplicationContextAware and

BeanNameAware”

ApplicationEventPublisherAwareEvent publisher of the enclosing

ApplicationContext

Section 5.15, “Additional

Capabilities of the

ApplicationContext”

BeanClassLoaderAware Class loader used to load the

bean classes.

the section called “Instantiating

beans”

BeanFactoryAware Declaring BeanFactory the section called

“ApplicationContextAware and

BeanNameAware”

BeanNameAware Name of the declaring bean the section called

“ApplicationContextAware and

BeanNameAware”

BootstrapContextAware Resource adapter

BootstrapContext the

container runs in. Typically

available only in JCA aware

ApplicationContexts

Chapter 26, JCA CCI

LoadTimeWeaverAware Defined weaver for processing

class definition at load time

the section called “Load-time

weaving with AspectJ in the

Spring Framework”

MessageSourceAware Configured strategy for

resolving messages (with

support for parametrization and

internationalization)

Section 5.15, “Additional

Capabilities of the

ApplicationContext”

NotificationPublisherAwareSpring JMX notification

publisher

Section 25.7, “Notifications”

PortletConfigAware Current PortletConfig

the container runs in. Valid

only in a web-aware Spring

ApplicationContext

Chapter 20, Portlet MVC

Framework

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 73

Name Injected Dependency Explained in…

PortletContextAware Current PortletContext

the container runs in. Valid

only in a web-aware Spring

ApplicationContext

Chapter 20, Portlet MVC

Framework

ResourceLoaderAware Configured loader for low-level

access to resources

Chapter 6, Resources

ServletConfigAware Current ServletConfig

the container runs in. Valid

only in a web-aware Spring

ApplicationContext

Chapter 17, Web MVC

framework

ServletContextAware Current ServletContext

the container runs in. Valid

only in a web-aware Spring

ApplicationContext

Chapter 17, Web MVC

framework

Note again that usage of these interfaces ties your code to the Spring API and does not follow

the Inversion of Control style. As such, they are recommended for infrastructure beans that require

programmatic access to the container.

5.7 Bean definition inheritance

A bean definition can contain a lot of configuration information, including constructor arguments, property

values, and container-specific information such as initialization method, static factory method name,

and so on. A child bean definition inherits configuration data from a parent definition. The child definition

can override some values, or add others, as needed. Using parent and child bean definitions can save

a lot of typing. Effectively, this is a form of templating.

If you work with an ApplicationContext interface programmatically, child bean definitions

are represented by the ChildBeanDefinition class. Most users do not work with

them on this level, instead configuring bean definitions declaratively in something like the

ClassPathXmlApplicationContext. When you use XML-based configuration metadata, you

indicate a child bean definition by using the parent attribute, specifying the parent bean as the value

of this attribute.

<bean id="inheritedTestBean" abstract="true"

class="org.springframework.beans.TestBean">

</bean>

<bean id="inheritsWithDifferentClass"

class="org.springframework.beans.DerivedTestBean"

parent="inheritedTestBean" init-method="initialize">

</bean>

A child bean definition uses the bean class from the parent definition if none is specified, but can also

override it. In the latter case, the child bean class must be compatible with the parent, that is, it must

accept the parent’s property values.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 74

A child bean definition inherits constructor argument values, property values, and method overrides

from the parent, with the option to add new values. Any initialization method, destroy method, and/or

static factory method settings that you specify will override the corresponding parent settings.

The remaining settings are always taken from the child definition: depends on, autowire mode,

dependency check, singleton, scope, lazy init.

The preceding example explicitly marks the parent bean definition as abstract by using the abstract

attribute. If the parent definition does not specify a class, explicitly marking the parent bean definition

as abstract is required, as follows:

</bean>

<bean id="inheritsWithClass" class="org.springframework.beans.DerivedTestBean"

parent="inheritedTestBeanWithoutClass" init-method="initialize">

</bean>

The parent bean cannot be instantiated on its own because it is incomplete, and it is also explicitly

marked as abstract. When a definition is abstract like this, it is usable only as a pure template

bean definition that serves as a parent definition for child definitions. Trying to use such an

abstract parent bean on its own, by referring to it as a ref property of another bean or doing an

explicit getBean() call with the parent bean id, returns an error. Similarly, the container’s internal

preInstantiateSingletons() method ignores bean definitions that are defined as abstract.

Note

ApplicationContext pre-instantiates all singletons by default. Therefore, it is important (at

least for singleton beans) that if you have a (parent) bean definition which you intend to use only

as a template, and this definition specifies a class, you must make sure to set the abstract attribute

to true, otherwise the application context will actually (attempt to) pre-instantiate the abstract

bean.

5.8 Container Extension Points

Typically, an application developer does not need to subclass ApplicationContext implementation

classes. Instead, the Spring IoC container can be extended by plugging in implementations of special

integration interfaces. The next few sections describe these integration interfaces.

Customizing beans using a BeanPostProcessor

The BeanPostProcessor interface defines callback methods that you can implement to provide your

own (or override the container’s default) instantiation logic, dependency-resolution logic, and so forth. If

you want to implement some custom logic after the Spring container finishes instantiating, configuring,

and initializing a bean, you can plug in one or more BeanPostProcessor implementations.

You can configure multiple BeanPostProcessor instances, and you can control the order in

which these BeanPostProcessors execute by setting the order property. You can set this

property only if the BeanPostProcessor implements the Ordered interface; if you write your own

BeanPostProcessor you should consider implementing the Ordered interface too. For further

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 75

details, consult the javadocs of the BeanPostProcessor and Ordered interfaces. See also the note

below on programmatic registration of BeanPostProcessors

Note

BeanPostProcessors operate on bean (or object) instances; that is to say, the Spring IoC

container instantiates a bean instance and then BeanPostProcessors do their work.

BeanPostProcessors are scoped per-container. This is only relevant if you are using container

hierarchies. If you define a BeanPostProcessor in one container, it will only post-process the

beans in that container. In other words, beans that are defined in one container are not post-

processed by a BeanPostProcessor defined in another container, even if both containers are

part of the same hierarchy.

To change the actual bean definition (i.e., the blueprint that defines the bean), you instead

need to use a BeanFactoryPostProcessor as described in the section called “Customizing

configuration metadata with a BeanFactoryPostProcessor”.

The org.springframework.beans.factory.config.BeanPostProcessor interface consists

of exactly two callback methods. When such a class is registered as a post-processor with the container,

for each bean instance that is created by the container, the post-processor gets a callback from the

container both before container initialization methods (such as InitializingBean’s afterPropertiesSet()

and any declared init method) are called as well as after any bean initialization callbacks. The post-

processor can take any action with the bean instance, including ignoring the callback completely. A

bean post-processor typically checks for callback interfaces or may wrap a bean with a proxy. Some

Spring AOP infrastructure classes are implemented as bean post-processors in order to provide proxy-

wrapping logic.

An ApplicationContext automatically detects any beans that are defined in the configuration

metadata which implement the BeanPostProcessor interface. The ApplicationContext registers

these beans as post-processors so that they can be called later upon bean creation. Bean post-

processors can be deployed in the container just like any other beans.

Note that when declaring a BeanPostProcessor using an @Bean factory method on a configuration

class, the return type of the factory method should be the implementation class itself or at least

the org.springframework.beans.factory.config.BeanPostProcessor interface, clearly

indicating the post-processor nature of that bean. Otherwise, the ApplicationContext won’t be able

to autodetect it by type before fully creating it. Since a BeanPostProcessor needs to be instantiated

early in order to apply to the initialization of other beans in the context, this early type detection is critical.

Note

Programmatically registering BeanPostProcessors

While the recommended approach for BeanPostProcessor registration is through

ApplicationContext auto-detection (as described above), it is also possible to register them

programmatically against a ConfigurableBeanFactory using the addBeanPostProcessor

method. This can be useful when needing to evaluate conditional logic before registration,

or even for copying bean post processors across contexts in a hierarchy. Note however

that BeanPostProcessors added programmatically do not respect the Ordered interface.

Here it is the order of registration that dictates the order of execution. Note also that

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 76

BeanPostProcessors registered programmatically are always processed before those

registered through auto-detection, regardless of any explicit ordering.

Note

BeanPostProcessors and AOP auto-proxying

Classes that implement the BeanPostProcessor interface are special and are treated differently

by the container. All BeanPostProcessors and beans that they reference directly are

instantiated on startup, as part of the special startup phase of the ApplicationContext. Next,

all BeanPostProcessors are registered in a sorted fashion and applied to all further beans in the

container. Because AOP auto-proxying is implemented as a BeanPostProcessor itself, neither

BeanPostProcessors nor the beans they reference directly are eligible for auto-proxying, and

thus do not have aspects woven into them.

For any such bean, you should see an informational log message: "Bean foo is not eligible

for getting processed by all BeanPostProcessor interfaces (for example: not eligible for auto-

proxying)".

Note that if you have beans wired into your BeanPostProcessor using autowiring or

@Resource (which may fall back to autowiring), Spring might access unexpected beans when

searching for type-matching dependency candidates, and therefore make them ineligible for

auto-proxying or other kinds of bean post-processing. For example, if you have a dependency

annotated with @Resource where the field/setter name does not directly correspond to the

declared name of a bean and no name attribute is used, then Spring will access other beans for

matching them by type.

The following examples show how to write, register, and use BeanPostProcessors in an

ApplicationContext.

Example: Hello World, BeanPostProcessor-style

This first example illustrates basic usage. The example shows a custom BeanPostProcessor

implementation that invokes the toString() method of each bean as it is created by the container

and prints the resulting string to the system console.

Find below the custom BeanPostProcessor implementation class definition:

package scripting;

import org.springframework.beans.factory.config.BeanPostProcessor;

import org.springframework.beans.BeansException;

public class InstantiationTracingBeanPostProcessor implements BeanPostProcessor {

// simply return the instantiated bean as-is

public Object postProcessBeforeInitialization(Object bean,

String beanName) throws BeansException {

return bean; // we could potentially return any object reference here...

}

public Object postProcessAfterInitialization(Object bean,

String beanName) throws BeansException {

System.out.println("Bean " + beanName + " created : " + bean.toString());

return bean;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 77

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:lang="http://www.springframework.org/schema/lang"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/lang

http://www.springframework.org/schema/lang/spring-lang.xsd">

<lang:groovy id="messenger"

script-source="classpath:org/springframework/scripting/groovy/Messenger.groovy">

<lang:property name="message" value="Fiona Apple Is Just So Dreamy."/>

</lang:groovy>

<!--

when the above bean (messenger) is instantiated, this custom

BeanPostProcessor implementation will output the fact to the system console

-->

</beans>

Notice how the InstantiationTracingBeanPostProcessor is simply defined. It does not even

have a name, and because it is a bean it can be dependency-injected just like any other bean. (The

preceding configuration also defines a bean that is backed by a Groovy script. The Spring dynamic

language support is detailed in the chapter entitled Chapter 29, Dynamic language support.)

The following simple Java application executes the preceding code and configuration:

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import org.springframework.scripting.Messenger;

public final class Boot {

public static void main(final String[] args) throws Exception {

ApplicationContext ctx = new ClassPathXmlApplicationContext("scripting/beans.xml");

Messenger messenger = (Messenger) ctx.getBean("messenger");

System.out.println(messenger);

}

The output of the preceding application resembles the following:

Bean messenger created : org.springframework.scripting.groovy.GroovyMessenger@272961

org.springframework.scripting.groovy.GroovyMessenger@272961

Example: The RequiredAnnotationBeanPostProcessor

Using callback interfaces or annotations in conjunction with a custom BeanPostProcessor

implementation is a common means of extending the Spring IoC container. An example is Spring’s

RequiredAnnotationBeanPostProcessor - a BeanPostProcessor implementation that ships

with the Spring distribution which ensures that JavaBean properties on beans that are marked with an

(arbitrary) annotation are actually (configured to be) dependency-injected with a value.

Customizing configuration metadata with a BeanFactoryPostProcessor

The next extension point that we will look at is

the org.springframework.beans.factory.config.BeanFactoryPostProcessor. The

semantics of this interface are similar to those of the BeanPostProcessor, with one major difference:

BeanFactoryPostProcessor operates on the bean configuration metadata; that is, the Spring IoC

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 78

container allows a BeanFactoryPostProcessor to read the configuration metadata and potentially

change it before the container instantiates any beans other than BeanFactoryPostProcessors.

You can configure multiple BeanFactoryPostProcessors, and you can control the order in which

these BeanFactoryPostProcessors execute by setting the order property. However, you can only

set this property if the BeanFactoryPostProcessor implements the Ordered interface. If you write

your own BeanFactoryPostProcessor, you should consider implementing the Ordered interface

too. Consult the javadocs of the BeanFactoryPostProcessor and Ordered interfaces for more

details.

Note

If you want to change the actual bean instances (i.e., the objects that are created from the

configuration metadata), then you instead need to use a BeanPostProcessor (described

above in the section called “Customizing beans using a BeanPostProcessor”). While it is

technically possible to work with bean instances within a BeanFactoryPostProcessor (e.g.,

using BeanFactory.getBean()), doing so causes premature bean instantiation, violating the

standard container lifecycle. This may cause negative side effects such as bypassing bean post

processing.

Also, BeanFactoryPostProcessors are scoped per-container. This is only relevant if you are

using container hierarchies. If you define a BeanFactoryPostProcessor in one container, it

will only be applied to the bean definitions in that container. Bean definitions in one container

will not be post-processed by BeanFactoryPostProcessors in another container, even if both

containers are part of the same hierarchy.

A bean factory post-processor is executed automatically when it is declared inside an

ApplicationContext, in order to apply changes to the configuration metadata that

define the container. Spring includes a number of predefined bean factory post-processors,

such as PropertyOverrideConfigurer and PropertyPlaceholderConfigurer. A custom

BeanFactoryPostProcessor can also be used, for example, to register custom property editors.

An ApplicationContext automatically detects any beans that are deployed into it that implement

the BeanFactoryPostProcessor interface. It uses these beans as bean factory post-processors, at

the appropriate time. You can deploy these post-processor beans as you would any other bean.

Note

As with BeanPostProcessors , you typically do not want to configure

BeanFactoryPostProcessors for lazy initialization. If no other bean references a

Bean(Factory)PostProcessor, that post-processor will not get instantiated at all. Thus,

marking it for lazy initialization will be ignored, and the Bean(Factory)PostProcessor will be

instantiated eagerly even if you set the default-lazy-init attribute to true on the declaration

of your <beans /> element.

Example: the Class name substitution PropertyPlaceholderConfigurer

You use the PropertyPlaceholderConfigurer to externalize property values from a bean

definition in a separate file using the standard Java Properties format. Doing so enables the person

deploying an application to customize environment-specific properties such as database URLs and

passwords, without the complexity or risk of modifying the main XML definition file or files for the

container.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 79

Consider the following XML-based configuration metadata fragment, where a DataSource with

placeholder values is defined. The example shows properties configured from an external Properties

file. At runtime, a PropertyPlaceholderConfigurer is applied to the metadata that will replace

some properties of the DataSource. The values to replace are specified as placeholders of the form

${property-name} which follows the Ant / log4j / JSP EL style.

</bean>

<bean id="dataSource" destroy-method="close"

class="org.apache.commons.dbcp.BasicDataSource">

</bean>

The actual values come from another file in the standard Java Properties format:

jdbc.driverClassName=org.hsqldb.jdbcDriver

jdbc.url=jdbc:hsqldb:hsql://production:9002

jdbc.username=sa

jdbc.password=root

Therefore, the string ${jdbc.username} is replaced at runtime with the value sa, and

the same applies for other placeholder values that match keys in the properties file. The

PropertyPlaceholderConfigurer checks for placeholders in most properties and attributes of a

bean definition. Furthermore, the placeholder prefix and suffix can be customized.

With the context namespace introduced in Spring 2.5, it is possible to configure property placeholders

with a dedicated configuration element. One or more locations can be provided as a comma-separated

list in the location attribute.

<context:property-placeholder location="classpath:com/foo/jdbc.properties"/>

The PropertyPlaceholderConfigurer not only looks for properties in the Properties file you

specify. By default it also checks against the Java System properties if it cannot find a property in the

specified properties files. You can customize this behavior by setting the systemPropertiesMode

property of the configurer with one of the following three supported integer values:

•never (0): Never check system properties

•fallback (1): Check system properties if not resolvable in the specified properties files. This is the

default.

•override (2): Check system properties first, before trying the specified properties files. This allows

system properties to override any other property source.

Consult the PropertyPlaceholderConfigurer javadocs for more information.

Tip

You can use the PropertyPlaceholderConfigurer to substitute class names, which is

sometimes useful when you have to pick a particular implementation class at runtime. For

example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 80

<value>classpath:com/foo/strategy.properties</value>

</property>

<value>custom.strategy.class=com.foo.DefaultStrategy</value>

</property>

</bean>

If the class cannot be resolved at runtime to a valid class, resolution of the bean fails when

it is about to be created, which is during the preInstantiateSingletons() phase of an

ApplicationContext for a non-lazy-init bean.

Example: the PropertyOverrideConfigurer

The PropertyOverrideConfigurer, another bean factory post-processor, resembles the

PropertyPlaceholderConfigurer, but unlike the latter, the original definitions can have default

values or no values at all for bean properties. If an overriding Properties file does not have an entry

for a certain bean property, the default context definition is used.

Note that the bean definition is not aware of being overridden, so it is not immediately obvious

from the XML definition file that the override configurer is being used. In case of multiple

PropertyOverrideConfigurer instances that define different values for the same bean property,

the last one wins, due to the overriding mechanism.

Properties file configuration lines take this format:

beanName.property=value

For example:

dataSource.driverClassName=com.mysql.jdbc.Driver

dataSource.url=jdbc:mysql:mydb

This example file can be used with a container definition that contains a bean called dataSource, which

has driver and url properties.

Compound property names are also supported, as long as every component of the path except the

final property being overridden is already non-null (presumably initialized by the constructors). In this

example…

foo.fred.bob.sammy=123

i. the sammy property of the bob property of the fred property of the foo bean is set to the scalar

value 123.

Note

Specified override values are always literal values; they are not translated into bean references.

This convention also applies when the original value in the XML bean definition specifies a bean

reference.

With the context namespace introduced in Spring 2.5, it is possible to configure property overriding

with a dedicated configuration element:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 81

<context:property-override location="classpath:override.properties"/>

Customizing instantiation logic with a FactoryBean

Implement the org.springframework.beans.factory.FactoryBean interface for objects that

are themselves factories.

The FactoryBean interface is a point of pluggability into the Spring IoC container’s instantiation logic.

If you have complex initialization code that is better expressed in Java as opposed to a (potentially)

verbose amount of XML, you can create your own FactoryBean, write the complex initialization inside

that class, and then plug your custom FactoryBean into the container.

The FactoryBean interface provides three methods:

•Object getObject(): returns an instance of the object this factory creates. The instance can

possibly be shared, depending on whether this factory returns singletons or prototypes.

•boolean isSingleton(): returns true if this FactoryBean returns singletons, false otherwise.

•Class getObjectType(): returns the object type returned by the getObject() method or null

if the type is not known in advance.

The FactoryBean concept and interface is used in a number of places within the Spring Framework;

more than 50 implementations of the FactoryBean interface ship with Spring itself.

When you need to ask a container for an actual FactoryBean instance itself instead of the bean

it produces, preface the bean’s id with the ampersand symbol ( &) when calling the getBean()

method of the ApplicationContext. So for a given FactoryBean with an id of myBean, invoking

getBean("myBean") on the container returns the product of the FactoryBean; whereas, invoking

getBean("&myBean") returns the FactoryBean instance itself.

5.9 Annotation-based container configuration

Are annotations better than XML for configuring Spring?

The introduction of annotation-based configurations raised the question of whether this approach

is better than XML. The short answer is it depends. The long answer is that each approach has

its pros and cons, and usually it is up to the developer to decide which strategy suits them better.

Due to the way they are defined, annotations provide a lot of context in their declaration, leading

to shorter and more concise configuration. However, XML excels at wiring up components without

touching their source code or recompiling them. Some developers prefer having the wiring close

to the source while others argue that annotated classes are no longer POJOs and, furthermore,

that the configuration becomes decentralized and harder to control.

No matter the choice, Spring can accommodate both styles and even mix them together. It’s worth

pointing out that through its JavaConfig option, Spring allows annotations to be used in a non-

invasive way, without touching the target components source code and that in terms of tooling, all

configuration styles are supported by the Spring Tool Suite.

An alternative to XML setups is provided by annotation-based configuration which rely on the bytecode

metadata for wiring up components instead of angle-bracket declarations. Instead of using XML to

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 82

describe a bean wiring, the developer moves the configuration into the component class itself by using

annotations on the relevant class, method, or field declaration. As mentioned in the section called

“Example: The RequiredAnnotationBeanPostProcessor”, using a BeanPostProcessor in conjunction

with annotations is a common means of extending the Spring IoC container. For example, Spring

2.0 introduced the possibility of enforcing required properties with the @Required annotation. Spring

2.5 made it possible to follow that same general approach to drive Spring’s dependency injection.

Essentially, the @Autowired annotation provides the same capabilities as described in the section

called “Autowiring collaborators” but with more fine-grained control and wider applicability. Spring 2.5

also added support for JSR-250 annotations such as @PostConstruct, and @PreDestroy. Spring

3.0 added support for JSR-330 (Dependency Injection for Java) annotations contained in the javax.inject

package such as @Inject and @Named. Details about those annotations can be found in the relevant

section.

Note

Annotation injection is performed before XML injection, thus the latter configuration will override

the former for properties wired through both approaches.

As always, you can register them as individual bean definitions, but they can also be implicitly registered

by including the following tag in an XML-based Spring configuration (notice the inclusion of the context

namespace):

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:annotation-config/>

</beans>

(The implicitly registered post-processors include AutowiredAnnotationBeanPostProcessor,

CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor, as

well as the aforementioned RequiredAnnotationBeanPostProcessor.)

Note

<context:annotation-config/> only looks for annotations on beans in the same application

context in which it is defined. This means that, if you put <context:annotation-config/>

in a WebApplicationContext for a DispatcherServlet, it only checks for @Autowired

beans in your controllers, and not your services. See Section 17.2, “The DispatcherServlet” for

more information.

@Required

The @Required annotation applies to bean property setter methods, as in the following example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 83

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Required

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

This annotation simply indicates that the affected bean property must be populated at configuration time,

through an explicit property value in a bean definition or through autowiring. The container throws an

exception if the affected bean property has not been populated; this allows for eager and explicit failure,

avoiding NullPointerExceptions or the like later on. It is still recommended that you put assertions

into the bean class itself, for example, into an init method. Doing so enforces those required references

and values even when you use the class outside of a container.

@Autowired

As expected, you can apply the @Autowired annotation to "traditional" setter methods:

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Autowired

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

Note

JSR 330’s @Inject annotation can be used in place of Spring’s @Autowired annotation in the

examples below. See here for more details

You can also apply the annotation to methods with arbitrary names and/or multiple arguments:

public class MovieRecommender {

private MovieCatalog movieCatalog;

private CustomerPreferenceDao customerPreferenceDao;

@Autowired

public void prepare(MovieCatalog movieCatalog,

CustomerPreferenceDao customerPreferenceDao) {

this.movieCatalog = movieCatalog;

this.customerPreferenceDao = customerPreferenceDao;

}

// ...

}

You can apply @Autowired to constructors and fields:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 84

public class MovieRecommender {

@Autowired

private MovieCatalog movieCatalog;

private CustomerPreferenceDao customerPreferenceDao;

@Autowired

public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {

this.customerPreferenceDao = customerPreferenceDao;

}

// ...

}

It is also possible to provide all beans of a particular type from the ApplicationContext by adding

the annotation to a field or method that expects an array of that type:

public class MovieRecommender {

@Autowired

private MovieCatalog[] movieCatalogs;

// ...

}

The same applies for typed collections:

public class MovieRecommender {

private Set<MovieCatalog> movieCatalogs;

@Autowired

public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {

this.movieCatalogs = movieCatalogs;

}

// ...

}

Tip

Your beans can implement the org.springframework.core.Ordered interface or either use

the @Order or standard @Priority annotation if you want items in the array or list to be sorted

into a specific order.

Even typed Maps can be autowired as long as the expected key type is String. The Map values will

contain all beans of the expected type, and the keys will contain the corresponding bean names:

public class MovieRecommender {

private Map<String, MovieCatalog> movieCatalogs;

@Autowired

public void setMovieCatalogs(Map<String, MovieCatalog> movieCatalogs) {

this.movieCatalogs = movieCatalogs;

}

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 85

By default, the autowiring fails whenever zero candidate beans are available; the default behavior is to

treat annotated methods, constructors, and fields as indicating required dependencies. This behavior

can be changed as demonstrated below.

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Autowired(required=false)

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

Note

Only one annotated constructor per-class can be marked as required, but multiple non-required

constructors can be annotated. In that case, each is considered among the candidates and Spring

uses the greediest constructor whose dependencies can be satisfied, that is the constructor that

has the largest number of arguments.

@Autowired's required attribute is recommended over the @Required annotation. The required

attribute indicates that the property is not required for autowiring purposes, the property is ignored

if it cannot be autowired. @Required, on the other hand, is stronger in that it enforces the property

that was set by any means supported by the container. If no value is injected, a corresponding

exception is raised.

You can also use @Autowired for interfaces that are well-known resolvable

dependencies: BeanFactory, ApplicationContext, Environment, ResourceLoader,

ApplicationEventPublisher, and MessageSource. These interfaces and their extended

interfaces, such as ConfigurableApplicationContext or ResourcePatternResolver, are

automatically resolved, with no special setup necessary.

public class MovieRecommender {

@Autowired

private ApplicationContext context;

public MovieRecommender() {

}

// ...

}

Note

@Autowired, @Inject, @Resource, and @Value annotations are handled by a Spring

BeanPostProcessor implementations which in turn means that you cannot apply these

annotations within your own BeanPostProcessor or BeanFactoryPostProcessor types (if

any). These types must be wired up explicitly via XML or using a Spring @Bean method.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 86

Fine-tuning annotation-based autowiring with qualifiers

Because autowiring by type may lead to multiple candidates, it is often necessary to have more control

over the selection process. One way to accomplish this is with Spring’s @Qualifier annotation. You

can associate qualifier values with specific arguments, narrowing the set of type matches so that a

specific bean is chosen for each argument. In the simplest case, this can be a plain descriptive value:

public class MovieRecommender {

@Autowired

@Qualifier("main")

private MovieCatalog movieCatalog;

// ...

}

The @Qualifier annotation can also be specified on individual constructor arguments or method

parameters:

public class MovieRecommender {

private MovieCatalog movieCatalog;

private CustomerPreferenceDao customerPreferenceDao;

@Autowired

public void prepare(@Qualifier("main")MovieCatalog movieCatalog,

CustomerPreferenceDao customerPreferenceDao) {

this.movieCatalog = movieCatalog;

this.customerPreferenceDao = customerPreferenceDao;

}

// ...

}

The corresponding bean definitions appear as follows. The bean with qualifier value "main" is wired with

the constructor argument that is qualified with the same value.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:annotation-config/>

</bean>

</bean>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 87

For a fallback match, the bean name is considered a default qualifier value. Thus you can define the bean

with an id "main" instead of the nested qualifier element, leading to the same matching result. However,

although you can use this convention to refer to specific beans by name, @Autowired is fundamentally

about type-driven injection with optional semantic qualifiers. This means that qualifier values, even with

the bean name fallback, always have narrowing semantics within the set of type matches; they do not

semantically express a reference to a unique bean id. Good qualifier values are "main" or "EMEA" or

"persistent", expressing characteristics of a specific component that are independent from the bean id,

which may be auto-generated in case of an anonymous bean definition like the one in the preceding

example.

Qualifiers also apply to typed collections, as discussed above, for example, to Set<MovieCatalog>. In

this case, all matching beans according to the declared qualifiers are injected as a collection. This implies

that qualifiers do not have to be unique; they rather simply constitute filtering criteria. For example, you

can define multiple MovieCatalog beans with the same qualifier value "action"; all of which would be

injected into a Set<MovieCatalog> annotated with @Qualifier("action").

Tip

If you intend to express annotation-driven injection by name, do not primarily use @Autowired,

even if is technically capable of referring to a bean name through @Qualifier values. Instead,

use the JSR-250 @Resource annotation, which is semantically defined to identify a specific target

component by its unique name, with the declared type being irrelevant for the matching process.

As a specific consequence of this semantic difference, beans that are themselves defined as a

collection or map type cannot be injected through @Autowired, because type matching is not

properly applicable to them. Use @Resource for such beans, referring to the specific collection

or map bean by unique name.

@Autowired applies to fields, constructors, and multi-argument methods, allowing for narrowing

through qualifier annotations at the parameter level. By contrast, @Resource is supported only

for fields and bean property setter methods with a single argument. As a consequence, stick with

qualifiers if your injection target is a constructor or a multi-argument method.

You can create your own custom qualifier annotations. Simply define an annotation and provide the

@Qualifier annotation within your definition:

@Target({ElementType.FIELD, ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

@Qualifier

public @interface Genre {

String value();

}

Then you can provide the custom qualifier on autowired fields and parameters:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 88

public class MovieRecommender {

@Autowired

@Genre("Action")

private MovieCatalog actionCatalog;

private MovieCatalog comedyCatalog;

@Autowired

public void setComedyCatalog(@Genre("Comedy") MovieCatalog comedyCatalog) {

this.comedyCatalog = comedyCatalog;

}

// ...

}

Next, provide the information for the candidate bean definitions. You can add <qualifier/> tags as

sub-elements of the <bean/> tag and then specify the type and value to match your custom qualifier

annotations. The type is matched against the fully-qualified class name of the annotation. Or, as a

convenience if no risk of conflicting names exists, you can use the short class name. Both approaches

are demonstrated in the following example.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:annotation-config/>

</bean>

_<qualifier type="example.Genre" value="Comedy"/>

</bean>

</beans>

In Section 5.10, “Classpath scanning and managed components”, you will see an annotation-based

alternative to providing the qualifier metadata in XML. Specifically, see the section called “Providing

qualifier metadata with annotations”.

In some cases, it may be sufficient to use an annotation without a value. This may be useful when

the annotation serves a more generic purpose and can be applied across several different types of

dependencies. For example, you may provide an offline catalog that would be searched when no Internet

connection is available. First define the simple annotation:

@Target({ElementType.FIELD, ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

@Qualifier

public @interface Offline {

}

Then add the annotation to the field or property to be autowired:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 89

public class MovieRecommender {

@Autowired

@Offline

private MovieCatalog offlineCatalog;

// ...

}

Now the bean definition only needs a qualifier type:

</bean>

You can also define custom qualifier annotations that accept named attributes in addition to or instead

of the simple value attribute. If multiple attribute values are then specified on a field or parameter

to be autowired, a bean definition must match all such attribute values to be considered an autowire

candidate. As an example, consider the following annotation definition:

@Target({ElementType.FIELD, ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

@Qualifier

public @interface MovieQualifier {

String genre();

Format format();

}

In this case Format is an enum:

public enum Format {

VHS, DVD, BLURAY

}

The fields to be autowired are annotated with the custom qualifier and include values for both attributes:

genre and format.

public class MovieRecommender {

@Autowired

@MovieQualifier(format=Format.VHS, genre="Action")

private MovieCatalog actionVhsCatalog;

@Autowired

@MovieQualifier(format=Format.VHS, genre="Comedy")

private MovieCatalog comedyVhsCatalog;

@Autowired

@MovieQualifier(format=Format.DVD, genre="Action")

private MovieCatalog actionDvdCatalog;

@Autowired

@MovieQualifier(format=Format.BLURAY, genre="Comedy")

private MovieCatalog comedyBluRayCatalog;

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 90

Finally, the bean definitions should contain matching qualifier values. This example also demonstrates

that bean meta attributes may be used instead of the <qualifier/> sub-elements. If available, the

<qualifier/> and its attributes take precedence, but the autowiring mechanism falls back on the

values provided within the <meta/> tags if no such qualifier is present, as in the last two bean definitions

in the following example.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:annotation-config/>

</qualifier>

</bean>

</qualifier>

</bean>

</bean>

</bean>

</beans>

Using generics as autowiring qualifiers

In addition to the @Qualifier annotation, it is also possible to use Java generic types as an implicit

form of qualification. For example, suppose you have the following configuration:

@Configuration

public class MyConfiguration {

@Bean

public StringStore stringStore() {

return new StringStore();

}

@Bean

public IntegerStore integerStore() {

return new IntegerStore();

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 91

Assuming that beans above implement a generic interface, i.e. Store<String> and

Store<Integer>, you can @Autowire the Store interface and the generic will be used as a qualifier:

@Autowired

private Store<String> s1; // <String> qualifier, injects the stringStore bean

@Autowired

private Store<Integer> s2; // <Integer> qualifier, injects the integerStore bean

Generic qualifiers also apply when autowiring Lists, Maps and Arrays:

// Inject all Store beans as long as they have an <Integer> generic

// Store<String> beans will not appear in this list

@Autowired

private List<Store<Integer>> s;

CustomAutowireConfigurer

The CustomAutowireConfigurer is a BeanFactoryPostProcessor that enables you to register

your own custom qualifier annotation types even if they are not annotated with Spring’s @Qualifier

annotation.

<bean id="customAutowireConfigurer"

class="org.springframework.beans.factory.annotation.CustomAutowireConfigurer">

<set>

<value>example.CustomQualifier</value>

</set>

</property>

</bean>

The AutowireCandidateResolver determines autowire candidates by:

• the autowire-candidate value of each bean definition

• any default-autowire-candidates pattern(s) available on the <beans/> element

• the presence of @Qualifier annotations and any custom annotations registered with the

CustomAutowireConfigurer

When multiple beans qualify as autowire candidates, the determination of a "primary" is the following:

if exactly one bean definition among the candidates has a primary attribute set to true, it will be

selected.

@Resource

Spring also supports injection using the JSR-250 @Resource annotation on fields or bean property

setter methods. This is a common pattern in Java EE 5 and 6, for example in JSF 1.2 managed beans

or JAX-WS 2.0 endpoints. Spring supports this pattern for Spring-managed objects as well.

@Resource takes a name attribute, and by default Spring interprets that value as the bean name to be

injected. In other words, it follows by-name semantics, as demonstrated in this example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 92

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Resource(name="myMovieFinder")

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

If no name is specified explicitly, the default name is derived from the field name or setter method. In

case of a field, it takes the field name; in case of a setter method, it takes the bean property name. So

the following example is going to have the bean with name "movieFinder" injected into its setter method:

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Resource

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

Note

The name provided with the annotation is resolved as a bean name by the

ApplicationContext of which the CommonAnnotationBeanPostProcessor is aware. The

names can be resolved through JNDI if you configure Spring’s SimpleJndiBeanFactory

explicitly. However, it is recommended that you rely on the default behavior and simply use

Spring’s JNDI lookup capabilities to preserve the level of indirection.

In the exclusive case of @Resource usage with no explicit name specified, and similar to @Autowired,

@Resource finds a primary type match instead of a specific named bean and resolves well-

known resolvable dependencies: the BeanFactory, ApplicationContext, ResourceLoader,

ApplicationEventPublisher, and MessageSource interfaces.

Thus in the following example, the customerPreferenceDao field first looks for a bean

named customerPreferenceDao, then falls back to a primary type match for the type

CustomerPreferenceDao. The "context" field is injected based on the known resolvable dependency

type ApplicationContext.

public class MovieRecommender {

@Resource

private CustomerPreferenceDao customerPreferenceDao;

@Resource

private ApplicationContext context;

public MovieRecommender() {

}

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 93

@PostConstruct and @PreDestroy

The CommonAnnotationBeanPostProcessor not only recognizes the @Resource annotation

but also the JSR-250 lifecycle annotations. Introduced in Spring 2.5, the support for these

annotations offers yet another alternative to those described in initialization callbacks and destruction

callbacks. Provided that the CommonAnnotationBeanPostProcessor is registered within the Spring

ApplicationContext, a method carrying one of these annotations is invoked at the same point in the

lifecycle as the corresponding Spring lifecycle interface method or explicitly declared callback method.

In the example below, the cache will be pre-populated upon initialization and cleared upon destruction.

public class CachingMovieLister {

@PostConstruct

public void populateMovieCache() {

// populates the movie cache upon initialization...

}

@PreDestroy

public void clearMovieCache() {

// clears the movie cache upon destruction...

}

Note

For details about the effects of combining various lifecycle mechanisms, see the section called

“Combining lifecycle mechanisms”.

5.10 Classpath scanning and managed components

Most examples in this chapter use XML to specify the configuration metadata that produces each

BeanDefinition within the Spring container. The previous section (Section 5.9, “Annotation-based

container configuration”) demonstrates how to provide a lot of the configuration metadata through

source-level annotations. Even in those examples, however, the "base" bean definitions are explicitly

defined in the XML file, while the annotations only drive the dependency injection. This section describes

an option for implicitly detecting the candidate components by scanning the classpath. Candidate

components are classes that match against a filter criteria and have a corresponding bean definition

registered with the container. This removes the need to use XML to perform bean registration, instead

you can use annotations (for example @Component), AspectJ type expressions, or your own custom

filter criteria to select which classes will have bean definitions registered with the container.

Note

Starting with Spring 3.0, many features provided by the Spring JavaConfig project are part of

the core Spring Framework. This allows you to define beans using Java rather than using the

traditional XML files. Take a look at the @Configuration, @Bean, @Import, and @DependsOn

annotations for examples of how to use these new features.

@Component and further stereotype annotations

The @Repository annotation is a marker for any class that fulfills the role or stereotype (also known as

Data Access Object or DAO) of a repository. Among the uses of this marker is the automatic translation

of exceptions as described in the section called “Exception translation”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 94

Spring provides further stereotype annotations: @Component, @Service, and @Controller.

@Component is a generic stereotype for any Spring-managed component. @Repository, @Service,

and @Controller are specializations of @Component for more specific use cases, for example,

in the persistence, service, and presentation layers, respectively. Therefore, you can annotate your

component classes with @Component, but by annotating them with @Repository, @Service, or

@Controller instead, your classes are more properly suited for processing by tools or associating

with aspects. For example, these stereotype annotations make ideal targets for pointcuts. It is also

possible that @Repository, @Service, and @Controller may carry additional semantics in future

releases of the Spring Framework. Thus, if you are choosing between using @Component or @Service

for your service layer, @Service is clearly the better choice. Similarly, as stated above, @Repository

is already supported as a marker for automatic exception translation in your persistence layer.

Meta-annotations

Many of the annotations provided by Spring can be used as "meta-annotations" in your own code. A

meta-annotation is simply an annotation, that can be applied to another annotation. For example, The

@Service annotation mentioned above is meta-annotated with with @Component:

@Target({ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

@Documented

@Component // Spring will see this and treat @Service in the same way as @Component

public @interface Service {

// ....

}

Meta-annotations can also be combined together to create composed annotations. For example,

the @RestController annotation from Spring MVC is composed of @Controller and

@ResponseBody.

With the exception of value(), meta-annotated types may redeclare attributes from the source

annotation to allow user customization. This can be particularly useful when you want to only expose

a subset of the source annotation attributes. For example, here is a custom @Scope annotation that

defines session scope, but still allows customization of the proxyMode.

@Target({ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

@Documented

@Scope("session")

public @interface SessionScope {

ScopedProxyMode proxyMode() default ScopedProxyMode.DEFAULT

}

Automatically detecting classes and registering bean definitions

Spring can automatically detect stereotyped classes and register corresponding BeanDefinitions

with the ApplicationContext. For example, the following two classes are eligible for such

autodetection:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 95

@Service

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Autowired

public SimpleMovieLister(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

@Repository

public class JpaMovieFinder implements MovieFinder {

// implementation elided for clarity

}

To autodetect these classes and register the corresponding beans, you need to add @ComponentScan

to your @Configuration class, where the basePackages attribute is a common parent package for

the two classes. (Alternatively, you can specify a comma-separated list that includes the parent package

of each class.)

@Configuration

@ComponentScan(basePackages = "org.example")

public class AppConfig {

...

}

Note

for concision, the above may have used the value attribute of the annotation, i.e.

ComponentScan("org.example")

The following is an alternative using XML

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:component-scan base-package="org.example"/>

</beans>

Tip

The use of <context:component-scan> implicitly enables the functionality of

<context:annotation-config>. There is usually no need to include the

<context:annotation-config> element when using <context:component-scan>.

Note

The scanning of classpath packages requires the presence of corresponding directory entries in

the classpath. When you build JARs with Ant, make sure that you do not activate the files-only

switch of the JAR task. Also, classpath directories may not get exposed based on security policies

in some environments, e.g. standalone apps on JDK 1.7.0_45 and higher (which requires Trusted-

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 96

Library setup in your manifests; see http://stackoverflow.com/questions/19394570/java-jre-7u45-

breaks-classloader-getresources).

Furthermore, the AutowiredAnnotationBeanPostProcessor and

CommonAnnotationBeanPostProcessor are both included implicitly when you use the component-

scan element. That means that the two components are autodetected and wired together - all without

any bean configuration metadata provided in XML.

Note

You can disable the registration of AutowiredAnnotationBeanPostProcessor and

CommonAnnotationBeanPostProcessor by including the annotation-config attribute with a

value of false.

Using filters to customize scanning

By default, classes annotated with @Component, @Repository, @Service, @Controller, or

a custom annotation that itself is annotated with @Component are the only detected candidate

components. However, you can modify and extend this behavior simply by applying custom filters. Add

them as includeFilters or excludeFilters parameters of the @ComponentScan annotation (or as include-

filter or exclude-filter sub-elements of the component-scan element). Each filter element requires the

type and expression attributes. The following table describes the filtering options.

Table 5.5. Filter Types

Filter Type Example Expression Description

annotation (default) org.example.SomeAnnotationAn annotation to be present

at the type level in target

components.

assignable org.example.SomeClass A class (or interface) that

the target components

are assignable to (extend/

implement).

aspectj org.example..*Service+ An AspectJ type expression

to be matched by the target

components.

regex org\.example\.Default.* A regex expression to be

matched by the target

components class names.

custom org.example.MyTypeFilter A custom implementation of the

org.springframework.core.type .TypeFilter

interface.

The following example shows the configuration ignoring all @Repository annotations and using "stub"

repositories instead.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 97

@Configuration

@ComponentScan(basePackages = "org.example",

includeFilters = @Filter(type = FilterType.REGEX, pattern = ".*Stub.*Repository"),

excludeFilters = @Filter(Repository.class))

public class AppConfig {

...

}

and the equivalent using XML

<beans>

<context:component-scan base-package="org.example">

<context:include-filter type="regex"

expression=".*Stub.*Repository"/>

<context:exclude-filter type="annotation"

expression="org.springframework.stereotype.Repository"/>

</context:component-scan>

</beans>

Note

You can also disable the default filters by setting useDefaultFilters=false on the annotation

or providing use-default-filters="false" as an attribute of the <component-scan/>

element. This will in effect disable automatic detection of classes annotated with @Component,

@Repository, @Service, or @Controller.

Defining bean metadata within components

Spring components can also contribute bean definition metadata to the container. You do this with the

same @Bean annotation used to define bean metadata within @Configuration annotated classes.

Here is a simple example:

@Component

public class FactoryMethodComponent {

@Bean

@Qualifier("public")

public TestBean publicInstance() {

return new TestBean("publicInstance");

}

public void doWork() {

// Component method implementation omitted

}

This class is a Spring component that has application-specific code contained in its doWork()

method. However, it also contributes a bean definition that has a factory method referring to the

method publicInstance(). The @Bean annotation identifies the factory method and other bean

definition properties, such as a qualifier value through the @Qualifier annotation. Other method level

annotations that can be specified are @Scope, @Lazy, and custom qualifier annotations.

Tip

In addition to its role for component initialization, the @Lazy annotation may also be placed on

injection points marked with @Autowired or @Inject. In this context, it leads to the injection

of a lazy-resolution proxy.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 98

Autowired fields and methods are supported as previously discussed, with additional support for

autowiring of @Bean methods:

@Component

public class FactoryMethodComponent {

private static int i;

@Bean

@Qualifier("public")

public TestBean publicInstance() {

return new TestBean("publicInstance");

}

// use of a custom qualifier and autowiring of method parameters

@Bean

protected TestBean protectedInstance(

@Qualifier("public") TestBean spouse,

@Value("#{privateInstance.age}") String country) {

TestBean tb = new TestBean("protectedInstance", 1);

tb.setSpouse(tb);

tb.setCountry(country);

return tb;

}

@Bean

@Scope(BeanDefinition.SCOPE_SINGLETON)

private TestBean privateInstance() {

return new TestBean("privateInstance", i++);

}

@Bean

@Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)

public TestBean requestScopedInstance() {

return new TestBean("requestScopedInstance", 3);

}

The example autowires the String method parameter country to the value of the Age property on

another bean named privateInstance. A Spring Expression Language element defines the value

of the property through the notation #{ <expression> }. For @Value annotations, an expression

resolver is preconfigured to look for bean names when resolving expression text.

The @Bean methods in a Spring component are processed differently than their counterparts inside

a Spring @Configuration class. The difference is that @Component classes are not enhanced

with CGLIB to intercept the invocation of methods and fields. CGLIB proxying is the means by which

invoking methods or fields within @Bean methods in @Configuration classes creates bean metadata

references to collaborating objects; such methods are not invoked with normal Java semantics. In

contrast, invoking a method or field in an @Bean method within a @Component class has standard Java

semantics.

Naming autodetected components

When a component is autodetected as part of the scanning process, its bean name is generated by the

BeanNameGenerator strategy known to that scanner. By default, any Spring stereotype annotation (

@Component, @Repository, @Service, and @Controller) that contains a name value will thereby

provide that name to the corresponding bean definition.

If such an annotation contains no name value or for any other detected component (such as those

discovered by custom filters), the default bean name generator returns the uncapitalized non-qualified

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 99

class name. For example, if the following two components were detected, the names would be

myMovieLister and movieFinderImpl:

@Service("myMovieLister")

public class SimpleMovieLister {

// ...

}

@Repository

public class MovieFinderImpl implements MovieFinder {

// ...

}

Note

If you do not want to rely on the default bean-naming strategy, you can provide a custom bean-

naming strategy. First, implement the BeanNameGenerator interface, and be sure to include

a default no-arg constructor. Then, provide the fully-qualified class name when configuring the

scanner:

@Configuration

@ComponentScan(basePackages = "org.example", nameGenerator = MyNameGenerator.class)

public class AppConfig {

...

}

<beans>

<context:component-scan base-package="org.example"

name-generator="org.example.MyNameGenerator" />

</beans>

As a general rule, consider specifying the name with the annotation whenever other components may be

making explicit references to it. On the other hand, the auto-generated names are adequate whenever

the container is responsible for wiring.

Providing a scope for autodetected components

As with Spring-managed components in general, the default and most common scope for autodetected

components is singleton. However, sometimes you need other scopes, which Spring 2.5 provides with

a new @Scope annotation. Simply provide the name of the scope within the annotation:

@Scope("prototype")

@Repository

public class MovieFinderImpl implements MovieFinder {

// ...

}

Note

To provide a custom strategy for scope resolution rather than relying on the annotation-based

approach, implement the ScopeMetadataResolver interface, and be sure to include a default

no-arg constructor. Then, provide the fully-qualified class name when configuring the scanner:

@Configuration

@ComponentScan(basePackages = "org.example", scopeResolver = MyScopeResolver.class)

public class AppConfig {

...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 100

<beans>

<context:component-scan base-package="org.example"

scope-resolver="org.example.MyScopeResolver" />

</beans>

When using certain non-singleton scopes, it may be necessary to generate proxies for the scoped

objects. The reasoning is described in the section called “Scoped beans as dependencies”. For this

purpose, a scoped-proxy attribute is available on the component-scan element. The three possible

values are: no, interfaces, and targetClass. For example, the following configuration will result in

standard JDK dynamic proxies:

@Configuration

@ComponentScan(basePackages = "org.example", scopedProxy = ScopedProxyMode.INTERFACES)

public class AppConfig {

...

}

<beans>

<context:component-scan base-package="org.example"

scoped-proxy="interfaces" />

</beans>

Providing qualifier metadata with annotations

The @Qualifier annotation is discussed in the section called “Fine-tuning annotation-based

autowiring with qualifiers”. The examples in that section demonstrate the use of the @Qualifier

annotation and custom qualifier annotations to provide fine-grained control when you resolve autowire

candidates. Because those examples were based on XML bean definitions, the qualifier metadata was

provided on the candidate bean definitions using the qualifier or meta sub-elements of the bean

element in the XML. When relying upon classpath scanning for autodetection of components, you

provide the qualifier metadata with type-level annotations on the candidate class. The following three

examples demonstrate this technique:

@Component

@Qualifier("Action")

public class ActionMovieCatalog implements MovieCatalog {

// ...

}

@Component

@Genre("Action")

public class ActionMovieCatalog implements MovieCatalog {

// ...

}

@Component

@Offline

public class CachingMovieCatalog implements MovieCatalog {

// ...

}

Note

As with most annotation-based alternatives, keep in mind that the annotation metadata is bound

to the class definition itself, while the use of XML allows for multiple beans of the same type

to provide variations in their qualifier metadata, because that metadata is provided per-instance

rather than per-class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 101

5.11 Using JSR 330 Standard Annotations

Starting with Spring 3.0, Spring offers support for JSR-330 standard annotations (Dependency

Injection). Those annotations are scanned in the same way as the Spring annotations. You just need

to have the relevant jars in your classpath.

Note

If you are using Maven, the javax.inject artifact is available in the standard Maven

repository ( http://repo1.maven.org/maven2/javax/inject/javax.inject/1/). You can add the following

dependency to your file pom.xml:

<groupId>javax.inject</groupId>

<artifactId>javax.inject</artifactId>

</dependency>

Dependency Injection with @Inject and @Named

Instead of @Autowired, @javax.inject.Inject may be used as follows:

import javax.inject.Inject;

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Inject

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

As with @Autowired, it is possible to use @Inject at the class-level, field-level, method-level and

constructor-argument level. If you would like to use a qualified name for the dependency that should be

injected, you should use the @Named annotation as follows:

import javax.inject.Inject;

import javax.inject.Named;

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Inject

public void setMovieFinder(@Named("main") MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

@Named: a standard equivalent to the @Component annotation

Instead of @Component, @javax.inject.Named may be used as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 102

import javax.inject.Inject;

import javax.inject.Named;

@Named("movieListener")

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Inject

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

It is very common to use @Component without specifying a name for the component. @Named can be

used in a similar fashion:

import javax.inject.Inject;

import javax.inject.Named;

@Named

public class SimpleMovieLister {

private MovieFinder movieFinder;

@Inject

public void setMovieFinder(MovieFinder movieFinder) {

this.movieFinder = movieFinder;

}

// ...

}

When using @Named, it is possible to use component-scanning in the exact same way as when using

Spring annotations:

@Configuration

@ComponentScan(basePackages = "org.example")

public class AppConfig {

...

}

Limitations of the standard approach

When working with standard annotations, it is important to know that some significant features are not

available as shown in the table below:

Table 5.6. Spring annotations vs. standard annotations

Spring javax.inject.* javax.inject restrictions /

comments

@Autowired @Inject @Inject has no required

attribute

@Component @Named -

@Scope("singleton") @Singleton The JSR-330 default scope

is like Spring’s prototype.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 103

Spring javax.inject.* javax.inject restrictions /

comments

However, in order to keep it

consistent with Spring’s general

defaults, a JSR-330 bean

declared in the Spring container

is a singleton by default. In

order to use a scope other than

singleton, you should use

Spring’s @Scope annotation.

javax.inject also provides

a @Scope annotation.

Nevertheless, this one is only

intended to be used for creating

your own annotations.

@Qualifier @Named -

@Value - no equivalent

@Required - no equivalent

@Lazy - no equivalent

5.12 Java-based container configuration

Basic concepts: @Bean and @Configuration

The central artifacts in Spring’s new Java-configuration support are @Configuration-annotated

classes and @Bean-annotated methods.

The @Bean annotation is used to indicate that a method instantiates, configures and initializes a

new object to be managed by the Spring IoC container. For those familiar with Spring’s <beans/>

XML configuration the @Bean annotation plays the same role as the <bean/> element. You can use

@Bean annotated methods with any Spring @Component, however, they are most often used with

@Configuration beans.

Annotating a class with @Configuration indicates that its primary purpose is as a source of bean

definitions. Furthermore, @Configuration classes allow inter-bean dependencies to be defined by

simply calling other @Bean methods in the same class. The simplest possible @Configuration class

would read as follows:

@Configuration

public class AppConfig {

@Bean

public MyService myService() {

return new MyServiceImpl();

}

The AppConfig class above would be equivalent to the following Spring <beans/> XML:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 104

<beans>

</beans>

The @Bean and @Configuration annotations will be discussed in depth in the sections below. First,

however, we’ll cover the various ways of creating a spring container using Java-based configuration.

Full @Configuration vs lite @Beans mode?

When @Bean methods are declared within classes that are not annotated with @Configuration

they are referred to as being processed in a lite mode. For example, bean methods declared in a

@Component or even in a plain old class will be considered lite.

Unlike full @Configuration, lite @Bean methods cannot easily declare inter-bean dependencies.

Usually one @Bean method should not invoke another @Bean method when operating in lite mode.

Only using @Bean methods within @Configuration classes is a recommended approach of

ensuring that full mode is always used. This will prevent the same @Bean method from accidentally

being invoked multiple times and helps to reduce subtle bugs that can be hard to track down when

operating in lite mode.

Instantiating the Spring container using

AnnotationConfigApplicationContext

The sections below document Spring’s AnnotationConfigApplicationContext, new in Spring

3.0. This versatile ApplicationContext implementation is capable of accepting not only

@Configuration classes as input, but also plain @Component classes and classes annotated with

JSR-330 metadata.

When @Configuration classes are provided as input, the @Configuration class itself is registered

as a bean definition, and all declared @Bean methods within the class are also registered as bean

definitions.

When @Component and JSR-330 classes are provided, they are registered as bean definitions, and it

is assumed that DI metadata such as @Autowired or @Inject are used within those classes where

necessary.

Simple construction

In much the same way that Spring XML files are used as input when instantiating a

ClassPathXmlApplicationContext, @Configuration classes may be used as input when

instantiating an AnnotationConfigApplicationContext. This allows for completely XML-free

usage of the Spring container:

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);

MyService myService = ctx.getBean(MyService.class);

myService.doStuff();

}

As mentioned above, AnnotationConfigApplicationContext is not limited to working only with

@Configuration classes. Any @Component or JSR-330 annotated class may be supplied as input

to the constructor. For example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 105

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(MyServiceImpl.class,

Dependency1.class, Dependency2.class);

MyService myService = ctx.getBean(MyService.class);

myService.doStuff();

}

The above assumes that MyServiceImpl, Dependency1 and Dependency2 use Spring dependency

injection annotations such as @Autowired.

Building the container programmatically using register(Class<?>…)

An AnnotationConfigApplicationContext may be instantiated using a no-arg constructor

and then configured using the register() method. This approach is particularly useful when

programmatically building an AnnotationConfigApplicationContext.

public static void main(String[] args) {

AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

ctx.register(AppConfig.class, OtherConfig.class);

ctx.register(AdditionalConfig.class);

ctx.refresh();

MyService myService = ctx.getBean(MyService.class);

myService.doStuff();

}

Enabling component scanning with scan(String…)

To enable component scanning, just annotate your @Configuration class as follows:

@Configuration

@ComponentScan(basePackages = "com.acme")

public class AppConfig {

...

}

Tip

Experienced Spring users will be familiar with the XML declaration equivalent from Spring’s

context: namespace

<beans>

<context:component-scan base-package="com.acme"/>

</beans>

In the example above, the com.acme package will be scanned, looking for any @Component-

annotated classes, and those classes will be registered as Spring bean definitions within the container.

AnnotationConfigApplicationContext exposes the scan(String...) method to allow for the

same component-scanning functionality:

public static void main(String[] args) {

AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

ctx.scan("com.acme");

ctx.refresh();

MyService myService = ctx.getBean(MyService.class);

}

Note

Remember that @Configuration classes are meta-annotated with @Component, so they

are candidates for component-scanning! In the example above, assuming that AppConfig is

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 106

declared within the com.acme package (or any package underneath), it will be picked up during

the call to scan(), and upon refresh() all its @Bean methods will be processed and registered

as bean definitions within the container.

Support for web applications with AnnotationConfigWebApplicationContext

A WebApplicationContext variant of AnnotationConfigApplicationContext is available

with AnnotationConfigWebApplicationContext. This implementation may be used

when configuring the Spring ContextLoaderListener servlet listener, Spring MVC

DispatcherServlet, etc. What follows is a web.xml snippet that configures a typical Spring MVC

web application. Note the use of the contextClass context-param and init-param:

<web-app>

<!-- Configure ContextLoaderListener to use AnnotationConfigWebApplicationContext

instead of the default XmlWebApplicationContext -->

<context-param>

<param-name>contextClass</param-name>

<param-value>

org.springframework.web.context.support.AnnotationConfigWebApplicationContext

</param-value>

</context-param>

<!-- Configuration locations must consist of one or more comma- or space-delimited

fully-qualified @Configuration classes. Fully-qualified packages may also be

specified for component-scanning -->

<context-param>

<param-name>contextConfigLocation</param-name>

<param-value>com.acme.AppConfig</param-value>

</context-param>

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

<servlet-name>dispatcher</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<!-- Configure DispatcherServlet to use AnnotationConfigWebApplicationContext

instead of the default XmlWebApplicationContext -->

<init-param>

<param-name>contextClass</param-name>

<param-value>

org.springframework.web.context.support.AnnotationConfigWebApplicationContext

</param-value>

</init-param>

<!-- Again, config locations must consist of one or more comma- or space-delimited

and fully-qualified @Configuration classes -->

<init-param>

<param-name>contextConfigLocation</param-name>

<param-value>com.acme.web.MvcConfig</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>dispatcher</servlet-name>

<url-pattern>/app/*</url-pattern>

</servlet-mapping>

</web-app>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 107

Using the @Bean annotation

@Bean is a method-level annotation and a direct analog of the XML <bean/> element. The annotation

supports some of the attributes offered by <bean/>, such as: init-method, destroy-method, autowiring

and name.

You can use the @Bean annotation in a @Configuration-annotated or in a @Component-annotated

class.

Declaring a bean

To declare a bean, simply annotate a method with the @Bean annotation. You use this method to register

a bean definition within an ApplicationContext of the type specified as the method’s return value.

By default, the bean name will be the same as the method name. The following is a simple example

of a @Bean method declaration:

@Configuration

public class AppConfig {

@Bean

public TransferService transferService() {

return new TransferServiceImpl();

}

The preceding configuration is exactly equivalent to the following Spring XML:

<beans>

</beans>

Both declarations make a bean named transferService available in the ApplicationContext,

bound to an object instance of type TransferServiceImpl:

transferService -> com.acme.TransferServiceImpl

Receiving lifecycle callbacks

Any classes defined with the @Bean annotation support the regular lifecycle callbacks and can use the

@PostConstruct and @PreDestroy annotations from JSR-250, see JSR-250 annotations for further

details.

The regular Spring lifecycle callbacks are fully supported as well. If a bean implements

InitializingBean, DisposableBean, or Lifecycle, their respective methods are called by the

container.

The standard set of *Aware interfaces such as BeanFactoryAware, BeanNameAware,

MessageSourceAware, ApplicationContextAware, and so on are also fully supported.

The @Bean annotation supports specifying arbitrary initialization and destruction callback methods,

much like Spring XML’s init-method and destroy-method attributes on the bean element:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 108

public class Foo {

public void init() {

// initialization logic

}

public class Bar {

public void cleanup() {

// destruction logic

}

@Configuration

public class AppConfig {

@Bean(initMethod = "init")

public Foo foo() {

return new Foo();

}

@Bean(destroyMethod = "cleanup")

public Bar bar() {

return new Bar();

}

Of course, in the case of Foo above, it would be equally as valid to call the init() method directly

during construction:

@Configuration

public class AppConfig {

@Bean

public Foo foo() {

Foo foo = new Foo();

foo.init();

return foo;

}

// ...

}

Tip

When you work directly in Java, you can do anything you like with your objects and do not always

need to rely on the container lifecycle!

Specifying bean scope

Using the @Scope annotation

You can specify that your beans defined with the @Bean annotation should have a specific scope. You

can use any of the standard scopes specified in the Bean Scopes section.

The default scope is singleton, but you can override this with the @Scope annotation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 109

@Configuration

public class MyConfiguration {

@Bean

@Scope("prototype")

public Encryptor encryptor() {

// ...

}

@Scope and scoped-proxy

Spring offers a convenient way of working with scoped dependencies through scoped proxies. The

easiest way to create such a proxy when using the XML configuration is the <aop:scoped-proxy/

> element. Configuring your beans in Java with a @Scope annotation offers equivalent support with

the proxyMode attribute. The default is no proxy ( ScopedProxyMode.NO), but you can specify

ScopedProxyMode.TARGET_CLASS or ScopedProxyMode.INTERFACES.

If you port the scoped proxy example from the XML reference documentation (see preceding link) to

our @Bean using Java, it would look like the following:

// an HTTP Session-scoped bean exposed as a proxy

@Bean

@Scope(value = "session", proxyMode = ScopedProxyMode.TARGET_CLASS)

public UserPreferences userPreferences() {

return new UserPreferences();

}

@Bean

public Service userService() {

UserService service = new SimpleUserService();

// a reference to the proxied userPreferences bean

service.setUserPreferences(userPreferences());

return service;

}

Customizing bean naming

By default, configuration classes use a @Bean method’s name as the name of the resulting bean. This

functionality can be overridden, however, with the name attribute.

@Configuration

public class AppConfig {

@Bean(name = "myFoo")

public Foo foo() {

return new Foo();

}

Bean aliasing

As discussed in the section called “Naming beans”, it is sometimes desirable to give a single bean

multiple names, otherwise known asbean aliasing. The name attribute of the @Bean annotation accepts

a String array for this purpose.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 110

@Configuration

public class AppConfig {

@Bean(name = { "dataSource", "subsystemA-dataSource", "subsystemB-dataSource" })

public DataSource dataSource() {

// instantiate, configure and return DataSource bean...

}

Bean description

Sometimes it is helpful to provide a more detailed textual description of a bean. This can be particularly

useful when beans are exposed (perhaps via JMX) for monitoring purposes.

To add a description to a @Bean the @Description annotation can be used:

@Configuration

public class AppConfig {

@Bean

@Desciption("Provides a basic example of a bean")

public Foo foo() {

return new Foo();

}

Using the @Configuration annotation

@Configuration is a class-level annotation indicating that an object is a source of bean definitions.

@Configuration classes declare beans via public @Bean annotated methods. Calls to @Bean

methods on @Configuration classes can also be used to define inter-bean dependencies. See the

section called “Basic concepts: @Bean and @Configuration” for a general introduction.

Injecting inter-bean dependencies

When @Beans have dependencies on one another, expressing that dependency is as simple as having

one bean method call another:

@Configuration

public class AppConfig {

@Bean

public Foo foo() {

return new Foo(bar());

}

@Bean

public Bar bar() {

return new Bar();

}

In the example above, the foo bean receives a reference to bar via constructor injection.

Note

This method of declaring inter-bean dependencies only works when the @Bean method is declared

within a @Configuration class. You cannot declare inter-bean dependencies using plain

@Component classes.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 111

Lookup method injection

As noted earlier, lookup method injection is an advanced feature that you should use rarely. It is useful

in cases where a singleton-scoped bean has a dependency on a prototype-scoped bean. Using Java

for this type of configuration provides a natural means for implementing this pattern.

public abstract class CommandManager {

public Object process(Object commandState) {

// grab a new instance of the appropriate Command interface

Command command = createCommand();

// set the state on the (hopefully brand new) Command instance

command.setState(commandState);

return command.execute();

}

// okay... but where is the implementation of this method?

protected abstract Command createCommand();

}

Using Java-configuration support , you can create a subclass of CommandManager where the abstract

createCommand() method is overridden in such a way that it looks up a new (prototype) command

object:

@Bean

@Scope("prototype")

public AsyncCommand asyncCommand() {

AsyncCommand command = new AsyncCommand();

// inject dependencies here as required

return command;

}

@Bean

public CommandManager commandManager() {

// return new anonymous implementation of CommandManager with command() overridden

// to return a new prototype Command object

return new CommandManager() {

protected Command createCommand() {

return asyncCommand();

}

Further information about how Java-based configuration works internally

The following example shows a @Bean annotated method being called twice:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 112

@Configuration

public class AppConfig {

@Bean

public ClientService clientService1() {

ClientServiceImpl clientService = new ClientServiceImpl();

clientService.setClientDao(clientDao());

return clientService;

}

@Bean

public ClientService clientService2() {

ClientServiceImpl clientService = new ClientServiceImpl();

clientService.setClientDao(clientDao());

return clientService;

}

@Bean

public ClientDao clientDao() {

return new ClientDaoImpl();

}

clientDao() has been called once in clientService1() and once in clientService2(). Since

this method creates a new instance of ClientDaoImpl and returns it, you would normally expect

having 2 instances (one for each service). That definitely would be problematic: in Spring, instantiated

beans have a singleton scope by default. This is where the magic comes in: All @Configuration

classes are subclassed at startup-time with CGLIB. In the subclass, the child method checks the

container first for any cached (scoped) beans before it calls the parent method and creates a new

instance. Note that as of Spring 3.2, it is no longer necessary to add CGLIB to your classpath because

CGLIB classes have been repackaged under org.springframework and included directly within the

spring-core JAR.

Note

The behavior could be different according to the scope of your bean. We are talking about

singletons here.

Note

There are a few restrictions due to the fact that CGLIB dynamically adds features at startup-time:

• Configuration classes should not be final

• They should have a constructor with no arguments

Composing Java-based configurations

Using the @Import annotation

Much as the <import/> element is used within Spring XML files to aid in modularizing configurations,

the @Import annotation allows for loading @Bean definitions from another configuration class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 113

@Configuration

public class ConfigA {

@Bean

public A a() {

return new A();

}

@Configuration

@Import(ConfigA.class)

public class ConfigB {

@Bean

public B b() {

return new B();

}

Now, rather than needing to specify both ConfigA.class and ConfigB.class when instantiating

the context, only ConfigB needs to be supplied explicitly:

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(ConfigB.class);

// now both beans A and B will be available...

A a = ctx.getBean(A.class);

B b = ctx.getBean(B.class);

}

This approach simplifies container instantiation, as only one class needs to be dealt with, rather than

requiring the developer to remember a potentially large number of @Configuration classes during

construction.

Injecting dependencies on imported @Bean definitions

The example above works, but is simplistic. In most practical scenarios, beans will have dependencies

on one another across configuration classes. When using XML, this is not an issue, per se, because

there is no compiler involved, and one can simply declare ref="someBean" and trust that Spring will

work it out during container initialization. Of course, when using @Configuration classes, the Java

compiler places constraints on the configuration model, in that references to other beans must be valid

Java syntax.

Fortunately, solving this problem is simple. Remember that @Configuration classes are ultimately

just another bean in the container - this means that they can take advantage of @Autowired injection

metadata just like any other bean!

Let’s consider a more real-world scenario with several @Configuration classes, each depending on

beans declared in the others:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 114

@Configuration

public class ServiceConfig {

@Autowired

private AccountRepository accountRepository;

@Bean

public TransferService transferService() {

return new TransferServiceImpl(accountRepository);

}

@Configuration

public class RepositoryConfig {

@Autowired

private DataSource dataSource;

@Bean

public AccountRepository accountRepository() {

return new JdbcAccountRepository(dataSource);

}

@Configuration

@Import({ServiceConfig.class, RepositoryConfig.class})

public class SystemTestConfig {

@Bean

public DataSource dataSource() {

// return new DataSource

}

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(SystemTestConfig.class);

// everything wires up across configuration classes...

TransferService transferService = ctx.getBean(TransferService.class);

transferService.transfer(100.00, "A123", "C456");

}

In the scenario above, using @Autowired works well and provides the desired modularity, but

determining exactly where the autowired bean definitions are declared is still somewhat ambiguous. For

example, as a developer looking at ServiceConfig, how do you know exactly where the @Autowired

AccountRepository bean is declared? It’s not explicit in the code, and this may be just fine.

Remember that the Spring Tool Suite provides tooling that can render graphs showing how everything

is wired up - that may be all you need. Also, your Java IDE can easily find all declarations and uses of

the AccountRepository type, and will quickly show you the location of @Bean methods that return

that type.

In cases where this ambiguity is not acceptable and you wish to have direct navigation from within

your IDE from one @Configuration class to another, consider autowiring the configuration classes

themselves:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 115

@Configuration

public class ServiceConfig {

@Autowired

private RepositoryConfig repositoryConfig;

@Bean

public TransferService transferService() {

// navigate through the config class to the @Bean method!

return new TransferServiceImpl(repositoryConfig.accountRepository());

}

In the situation above, it is completely explicit where AccountRepository is defined. However,

ServiceConfig is now tightly coupled to RepositoryConfig; that’s the tradeoff. This tight coupling

can be somewhat mitigated by using interface-based or abstract class-based @Configuration

classes. Consider the following:

@Configuration

public class ServiceConfig {

@Autowired

private RepositoryConfig repositoryConfig;

@Bean

public TransferService transferService() {

return new TransferServiceImpl(repositoryConfig.accountRepository());

}

@Configuration

public interface RepositoryConfig {

@Bean

AccountRepository accountRepository();

}

@Configuration

public class DefaultRepositoryConfig implements RepositoryConfig {

@Bean

public AccountRepository accountRepository() {

return new JdbcAccountRepository(...);

}

@Configuration

@Import({ServiceConfig.class, DefaultRepositoryConfig.class}) // import the concrete config!

public class SystemTestConfig {

@Bean

public DataSource dataSource() {

// return DataSource

}

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(SystemTestConfig.class);

TransferService transferService = ctx.getBean(TransferService.class);

transferService.transfer(100.00, "A123", "C456");

}

Now ServiceConfig is loosely coupled with respect to the concrete DefaultRepositoryConfig,

and built-in IDE tooling is still useful: it will be easy for the developer to get a type hierarchy of

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 116

RepositoryConfig implementations. In this way, navigating @Configuration classes and their

dependencies becomes no different than the usual process of navigating interface-based code.

Conditionally including @Configuration classes or @Beans

It is often useful to conditionally enable to disable a complete @Configuration class, or even individual

@Bean methods, based on some arbitrary system state. One common example of this it to use the

@Profile annotation to active beans only when a specific profile has been enabled in the Spring

Environment (see the section called “Bean definition profiles” for details).

The @Profile annotation is actually implemented using a much more flexible

annotation called @Conditional. The @Conditional annotation indicates specific

org.springframework.context.annotation.Condition implementations that should be

consulted before a @Bean is registered.

Implementations of the Condition interface simply provide a matches(...) method that returns

true or false. For example, here is the actual Condition implementation used for @Profile:

@Override

public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {

if (context.getEnvironment() != null) {

// Read the @Profile annotation attributes

MultiValueMap<String, Object> attrs =

metadata.getAllAnnotationAttributes(Profile.class.getName());

if (attrs != null) {

for (Object value : attrs.get("value")) {

if (context.getEnvironment().acceptsProfiles(((String[]) value))) {

return true;

}

return false;

}

return true;

}

See the @Conditional javadocs for more detail.

Combining Java and XML configuration

Spring’s @Configuration class support does not aim to be a 100% complete replacement for Spring

XML. Some facilities such as Spring XML namespaces remain an ideal way to configure the container.

In cases where XML is convenient or necessary, you have a choice: either instantiate the container in an

"XML-centric" way using, for example, ClassPathXmlApplicationContext, or in a "Java-centric"

fashion using AnnotationConfigApplicationContext and the @ImportResource annotation to

import XML as needed.

XML-centric use of @Configuration classes

It may be preferable to bootstrap the Spring container from XML and include @Configuration classes

in an ad-hoc fashion. For example, in a large existing codebase that uses Spring XML, it will be easier to

create @Configuration classes on an as-needed basis and include them from the existing XML files.

Below you’ll find the options for using @Configuration classes in this kind of "XML-centric" situation.

Remember that @Configuration classes are ultimately just bean definitions in the container. In this

example, we create a @Configuration class named AppConfig and include it within system-test-

config.xml as a <bean/> definition. Because <context:annotation-config/> is switched

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 117

on, the container will recognize the @Configuration annotation, and process the @Bean methods

declared in AppConfig properly.

@Configuration

public class AppConfig {

@Autowired

private DataSource dataSource;

@Bean

public AccountRepository accountRepository() {

return new JdbcAccountRepository(dataSource);

}

@Bean

public TransferService transferService() {

return new TransferService(accountRepository());

}

system-test-config.xml

<beans>

<context:annotation-config/>

<context:property-placeholder location="classpath:/com/acme/jdbc.properties"/>

</bean>

</beans>

jdbc.properties

jdbc.url=jdbc:hsqldb:hsql://localhost/xdb

jdbc.username=sa

jdbc.password=

public static void main(String[] args) {

ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:/com/acme/system-test-

config.xml");

TransferService transferService = ctx.getBean(TransferService.class);

// ...

}

Note

In system-test-config.xml above, the AppConfig<bean/> does not declare an id

element. While it would be acceptable to do so, it is unnecessary given that no other bean will ever

refer to it, and it is unlikely that it will be explicitly fetched from the container by name. Likewise

with the DataSource bean - it is only ever autowired by type, so an explicit bean id is not strictly

required.

Because @Configuration is meta-annotated with @Component, @Configuration-annotated

classes are automatically candidates for component scanning. Using the same scenario as above,

we can redefine system-test-config.xml to take advantage of component-scanning. Note that

in this case, we don’t need to explicitly declare <context:annotation-config/>, because

<context:component-scan/> enables all the same functionality.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 118

system-test-config.xml

<beans>

<context:component-scan base-package="com.acme"/>

<context:property-placeholder location="classpath:/com/acme/jdbc.properties"/>

</bean>

</beans>

@Configuration class-centric use of XML with @ImportResource

In applications where @Configuration classes are the primary mechanism for configuring the

container, it will still likely be necessary to use at least some XML. In these scenarios, simply use

@ImportResource and define only as much XML as is needed. Doing so achieves a "Java-centric"

approach to configuring the container and keeps XML to a bare minimum.

@Configuration

@ImportResource("classpath:/com/acme/properties-config.xml")

public class AppConfig {

@Value("${jdbc.url}")

private String url;

@Value("${jdbc.username}")

private String username;

@Value("${jdbc.password}")

private String password;

@Bean

public DataSource dataSource() {

return new DriverManagerDataSource(url, username, password);

}

properties-config.xml

<beans>

<context:property-placeholder location="classpath:/com/acme/jdbc.properties"/>

</beans>

jdbc.properties

jdbc.url=jdbc:hsqldb:hsql://localhost/xdb

jdbc.username=sa

jdbc.password=

public static void main(String[] args) {

ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);

TransferService transferService = ctx.getBean(TransferService.class);

// ...

}

5.13 Environment abstraction

The Environment is an abstraction integrated in the container that models two key aspects of the

application environment: profiles and properties.

A profile is a named, logical group of bean definitions to be registered with the container only if the given

profile is active. Beans may be assigned to a profile whether defined in XML or via annotations. The role

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 119

of the Environment object with relation to profiles is in determining which profiles (if any) are currently

active, and which profiles (if any) should be active by default.

Properties play an important role in almost all applications, and may originate from a variety of

sources: properties files, JVM system properties, system environment variables, JNDI, servlet context

parameters, ad-hoc Properties objects, Maps, and so on. The role of the Environment object with

relation to properties is to provide the user with a convenient service interface for configuring property

sources and resolving properties from them.

Bean definition profiles

Bean definition profiles is a mechanism in the core container that allows for registration of different beans

in different environments. The word environment can mean different things to different users and this

feature can help with many use cases, including:

• working against an in-memory datasource in development vs looking up that same datasource from

JNDI when in QA or production

• registering monitoring infrastructure only when deploying an application into a performance

environment

• registering customized implementations of beans for customer A vs. customer B deployments

Let’s consider the first use case in a practical application that requires a DataSource. In a test

environment, the configuration may look like this:

@Bean

public DataSource dataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("my-schema.sql")

.addScript("my-test-data.sql")

.build();

}

Let’s now consider how this application will be deployed into a QA or production environment, assuming

that the datasource for the application will be registered with the production application server’s JNDI

directory. Our dataSource bean now looks like this:

@Bean

public DataSource dataSource() throws Exception {

Context ctx = new InitialContext();

return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");

}

The problem is how to switch between using these two variations based on the current environment.

Over time, Spring users have devised a number of ways to get this done, usually relying on a combination

of system environment variables and XML <import/> statements containing ${placeholder}

tokens that resolve to the correct configuration file path depending on the value of an environment

variable. Bean definition profiles is a core container feature that provides a solution to this problem.

If we generalize the example use case above of environment-specific bean definitions, we end up with

the need to register certain bean definitions in certain contexts, while not in others. You could say that

you want to register a certain profile of bean definitions in situation A, and a different profile in situation

B. Let’s first see how we can update our configuration to reflect this need.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 120

@Profile

The @Profile annotation allows to indicate that a component is eligible for registration when one

or more specified profiles are active. Using our example above, we can rewrite the dataSource

configuration as follows:

@Configuration

@Profile("dev")

public class StandaloneDataConfig {

@Bean

public DataSource dataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("classpath:com/bank/config/sql/schema.sql")

.addScript("classpath:com/bank/config/sql/test-data.sql")

.build();

}

@Configuration

@Profile("production")

public class JndiDataConfig {

@Bean

public DataSource dataSource() throws Exception {

Context ctx = new InitialContext();

return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");

}

@Profile can be used as a meta-annotation, for the purpose of composing custom stereotype

annotations. The following example defines a @Production custom annotation that can be used as a

drop-in replacement of @Profile("production"):

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@Profile("production")

public @interface Production {

}

@Profile can also be specified at method-level to include only one particular bean of a configuration

class:

@Configuration

public class AppConfig {

@Bean

@Profile("dev")

public DataSource devDataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("classpath:com/bank/config/sql/schema.sql")

.addScript("classpath:com/bank/config/sql/test-data.sql")

.build();

}

@Bean

@Profile("production")

public DataSource productionDataSource() throws Exception {

Context ctx = new InitialContext();

return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 121

Tip

If a @Configuration class is marked with @Profile, all of the @Bean methods and @Import

annotations associated with that class will be bypassed unless one or more of the specified profiles

are active. If a @Component or @Configuration class is marked with @Profile({"p1",

"p2"}), that class will not be registered/ processed unless profiles p1 and/or p2 have been

activated. If a given profile is prefixed with the NOT operator (!), the annotated element will be

registered if the profile is not active. e.g., for @Profile({"p1", "!p2"}), registration will occur

if profile p1 is active or if profile p2 is not active.

XML Bean definition profiles

The XML counterpart is an update of the beans element that accepts a profile attribute. Our sample

configuration above can be rewritten in two XML files as follows:

<beans profile="dev"

xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:jdbc="http://www.springframework.org/schema/jdbc"

xsi:schemaLocation="...">

<jdbc:embedded-database id="dataSource">

<jdbc:script location="classpath:com/bank/config/sql/schema.sql"/>

<jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/>

</jdbc:embedded-database>

</beans>

<beans profile="production"

xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:jee="http://www.springframework.org/schema/jee"

xsi:schemaLocation="...">

<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>

</beans>

It is also possible to avoid that split and nest <beans/> elements within the same file:

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:jdbc="http://www.springframework.org/schema/jdbc"

xmlns:jee="http://www.springframework.org/schema/jee"

xsi:schemaLocation="...">

<jdbc:embedded-database id="dataSource">

<jdbc:script location="classpath:com/bank/config/sql/schema.sql"/>

<jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/>

</jdbc:embedded-database>

</beans>

<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>

</beans>

The spring-bean.xsd has been constrained to allow such elements only as the last ones in the file.

This should help provide flexibility without incurring clutter in the XML files.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 122

Enabling a profile

Now that we have updated our configuration, we still need to instruct which profile is active. If we started

our sample application right now, we would see a NoSuchBeanDefinitionException thrown,

because the container could not find the Spring bean named dataSource.

Activating a profile can be done in several ways, but the most straightforward is to do it programmatically

against the ApplicationContext API:

AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();

ctx.getEnvironment().setActiveProfiles("dev");

ctx.register(SomeConfig.class, StandaloneDataConfig.class, JndiDataConfig.class);

ctx.refresh();

In addition, profiles may also be activated declaratively through the spring.profiles.active

property which may be specified through system environment variables, JVM system properties, servlet

context parameters in web.xml or even as an entry in JNDI (see the section called “PropertySource

Abstraction”).

Note that profiles are not an "either-or" proposition; it is possible to activate multiple profiles at once.

Programmatically, simply provide multiple profile names to the setActiveProfiles() method, which

accepts String... varargs:

ctx.getEnvironment().setActiveProfiles("profile1", "profile2");

Declaratively, spring.profiles.active may accept a comma-separated list of profile names:

-Dspring.profiles.active="profile1,profile2"

Default profile

The default profile represents the profile that is enabled by default. Consider the following:

@Configuration

@Profile("default")

public class DefaultDataConfig {

@Bean

public DataSource dataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("classpath:com/bank/config/sql/schema.sql")

.build();

}

If no profile is active, the dataSource above will be created; this can be seen as a way to provide a

default definition for one or more beans. If any profile is enabled, the default profile will not apply.

The name of that default profile can be changed using setDefaultProfiles on the Environment

or declaratively using the spring.profiles.default property.

PropertySource Abstraction

Spring’s Environment abstraction provides search operations over a configurable hierarchy of property

sources. To explain fully, consider the following:

ApplicationContext ctx = new GenericApplicationContext();

Environment env = ctx.getEnvironment();

boolean containsFoo = env.containsProperty("foo");

System.out.println("Does my environment contain the foo property? " + containsFoo);

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 123

In the snippet above, we see a high-level way of asking Spring whether the foo property is defined for the

current environment. To answer this question, the Environment object performs a search over a set of

PropertySource objects. A PropertySource is a simple abstraction over any source of key-value

pairs, and Spring’s StandardEnvironment is configured with two PropertySource objects — one

representing the set of JVM system properties (a la System.getProperties()) and one representing

the set of system environment variables (a la System.getenv()).

Note

These default property sources are present for StandardEnvironment, for use in

standalone applications. StandardServletEnvironment is populated with additional

default property sources including servlet config and servlet context parameters.

StandardPortletEnvironment similarly has access to portlet config and portlet context

parameters as property sources. Both can optionally enable a JndiPropertySource. See

Javadoc for details.

Concretely, when using the StandardEnvironment, the call to env.containsProperty("foo")

will return true if a foo system property or foo environment variable is present at runtime.

Tip

The search performed is hierarchical. By default, system properties have precedence over

environment variables, so if the foo property happens to be set in both places during a call to

env.getProperty("foo"), the system property value will win and be returned preferentially

over the environment variable.

Most importantly, the entire mechanism is configurable. Perhaps you have a custom source of properties

that you’d like to integrate into this search. No problem — simply implement and instantiate your own

PropertySource and add it to the set of PropertySources for the current Environment:

ConfigurableApplicationContext ctx = new GenericApplicationContext();

MutablePropertySources sources = ctx.getEnvironment().getPropertySources();

sources.addFirst(new MyPropertySource());

In the code above, MyPropertySource has been added with highest precedence in the search. If

it contains a foo property, it will be detected and returned ahead of any foo property in any other

PropertySource. The MutablePropertySources API exposes a number of methods that allow for

precise manipulation of the set of property sources.

@PropertySource

The @PropertySource annotation provides a convenient and declarative mechanism for adding a

PropertySource to Spring’s Environment.

Given a file "app.properties" containing the key/value pair testbean.name=myTestBean, the

following @Configuration class uses @PropertySource in such a way that a call to

testBean.getName() will return "myTestBean".

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 124

@Configuration

@PropertySource("classpath:/com/myco/app.properties")

public class AppConfig {

@Autowired

Environment env;

@Bean

public TestBean testBean() {

TestBean testBean = new TestBean();

testBean.setName(env.getProperty("testbean.name"));

return testBean;

}

Any ${...} placeholders present in a @PropertySource resource location will be resolved against

the set of property sources already registered against the environment. For example:

@Configuration

@PropertySource("classpath:/com/${my.placeholder:default/path}/app.properties")

public class AppConfig {

@Autowired

Environment env;

@Bean

public TestBean testBean() {

TestBean testBean = new TestBean();

testBean.setName(env.getProperty("testbean.name"));

return testBean;

}

Assuming that "my.placeholder" is present in one of the property sources already registered, e.g. system

properties or environment variables, the placeholder will be resolved to the corresponding value. If not,

then "default/path" will be used as a default. If no default is specified and a property cannot be resolved,

an IllegalArgumentException will be thrown.

Placeholder resolution in statements

Historically, the value of placeholders in elements could be resolved only against JVM system properties

or environment variables. No longer is this the case. Because the Environment abstraction is integrated

throughout the container, it’s easy to route resolution of placeholders through it. This means that you

may configure the resolution process in any way you like: change the precedence of searching through

system properties and environment variables, or remove them entirely; add your own property sources

to the mix as appropriate.

Concretely, the following statement works regardless of where the customer property is defined, as

long as it is available in the Environment:

<beans>

</beans>

5.14 Registering a LoadTimeWeaver

The LoadTimeWeaver is used by Spring to dynamically transform classes as they are loaded into the

Java virtual machine (JVM).

To enable load-time weaving add the @EnableLoadTimeWeaving to one of your @Configuration

classes:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 125

@Configuration

@EnableLoadTimeWeaving

public class AppConfig {

}

Alternatively for XML configuration use the context:load-time-weaver element:

<beans>

<context:load-time-weaver/>

</beans>

Once configured for the ApplicationContext. Any bean within that ApplicationContext

may implement LoadTimeWeaverAware, thereby receiving a reference to the load-time

weaver instance. This is particularly useful in combination with Spring’s JPA support

where load-time weaving may be necessary for JPA class transformation. Consult the

LocalContainerEntityManagerFactoryBean javadocs for more detail. For more on AspectJ

load-time weaving, see the section called “Load-time weaving with AspectJ in the Spring Framework”.

5.15 Additional Capabilities of the ApplicationContext

As was discussed in the chapter introduction, the org.springframework.beans.factory package

provides basic functionality for managing and manipulating beans, including in a programmatic

way. The org.springframework.context package adds the ApplicationContext interface,

which extends the BeanFactory interface, in addition to extending other interfaces to provide

additional functionality in a more application framework-oriented style. Many people use the

ApplicationContext in a completely declarative fashion, not even creating it programmatically,

but instead relying on support classes such as ContextLoader to automatically instantiate an

ApplicationContext as part of the normal startup process of a Java EE web application.

To enhance BeanFactory functionality in a more framework-oriented style the context package also

provides the following functionality:

•Access to messages in i18n-style, through the MessageSource interface.

•Access to resources, such as URLs and files, through the ResourceLoader interface.

•Event publication to beans implementing the ApplicationListener interface, through the use of

the ApplicationEventPublisher interface.

•Loading of multiple (hierarchical) contexts, allowing each to be focused on one particular layer, such

as the web layer of an application, through the HierarchicalBeanFactory interface.

Internationalization using MessageSource

The ApplicationContext interface extends an interface called MessageSource, and

therefore provides internationalization (i18n) functionality. Spring also provides the interface

HierarchicalMessageSource, which can resolve messages hierarchically. Together these

interfaces provide the foundation upon which Spring effects message resolution. The methods defined

on these interfaces include:

•String getMessage(String code, Object[] args, String default, Locale loc):

The basic method used to retrieve a message from the MessageSource. When no message is found

for the specified locale, the default message is used. Any arguments passed in become replacement

values, using the MessageFormat functionality provided by the standard library.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 126

•String getMessage(String code, Object[] args, Locale loc): Essentially the same

as the previous method, but with one difference: no default message can be specified; if the message

cannot be found, a NoSuchMessageException is thrown.

•String getMessage(MessageSourceResolvable resolvable, Locale locale):

All properties used in the preceding methods are also wrapped in a class named

MessageSourceResolvable, which you can use with this method.

When an ApplicationContext is loaded, it automatically searches for a MessageSource bean

defined in the context. The bean must have the name messageSource. If such a bean is found, all

calls to the preceding methods are delegated to the message source. If no message source is found,

the ApplicationContext attempts to find a parent containing a bean with the same name. If it does,

it uses that bean as the MessageSource. If the ApplicationContext cannot find any source for

messages, an empty DelegatingMessageSource is instantiated in order to be able to accept calls

to the methods defined above.

Spring provides two MessageSource implementations, ResourceBundleMessageSource and

StaticMessageSource. Both implement HierarchicalMessageSource in order to do nested

messaging. The StaticMessageSource is rarely used but provides programmatic ways to add

messages to the source. The ResourceBundleMessageSource is shown in the following example:

<beans>

<bean id="messageSource"

class="org.springframework.context.support.ResourceBundleMessageSource">

<list>

<value>format</value>

<value>exceptions</value>

<value>windows</value>

</list>

</property>

</bean>

</beans>

In the example it is assumed you have three resource bundles defined in your classpath called format,

exceptions and windows. Any request to resolve a message will be handled in the JDK standard

way of resolving messages through ResourceBundles. For the purposes of the example, assume the

contents of two of the above resource bundle files are…

# in format.properties

message=Alligators rock!

# in exceptions.properties

argument.required=The {0} argument is required.

A program to execute the MessageSource functionality is shown in the next example. Remember that

all ApplicationContext implementations are also MessageSource implementations and so can be

cast to the MessageSource interface.

public static void main(String[] args) {

MessageSource resources = new ClassPathXmlApplicationContext("beans.xml");

String message = resources.getMessage("message", null, "Default", null);

System.out.println(message);

}

The resulting output from the above program will be…

Alligators rock!

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 127

So to summarize, the MessageSource is defined in a file called beans.xml, which exists at the root of

your classpath. The messageSource bean definition refers to a number of resource bundles through

its basenames property. The three files that are passed in the list to the basenames property exist as

files at the root of your classpath and are called format.properties, exceptions.properties,

and windows.properties respectively.

The next example shows arguments passed to the message lookup; these arguments will be converted

into Strings and inserted into placeholders in the lookup message.

<beans>

</bean>

</bean>

</beans>

public class Example {

private MessageSource messages;

public void setMessages(MessageSource messages) {

this.messages = messages;

}

public void execute() {

String message = this.messages.getMessage("argument.required",

new Object [] {"userDao"}, "Required", null);

System.out.println(message);

}

The resulting output from the invocation of the execute() method will be…

The userDao argument is required.

With regard to internationalization (i18n), Spring’s various MessageResource implementations follow

the same locale resolution and fallback rules as the standard JDK ResourceBundle. In short, and

continuing with the example messageSource defined previously, if you want to resolve messages

against the British (en-GB) locale, you would create files called format_en_GB.properties,

exceptions_en_GB.properties, and windows_en_GB.properties respectively.

Typically, locale resolution is managed by the surrounding environment of the application. In this

example, the locale against which (British) messages will be resolved is specified manually.

# in exceptions_en_GB.properties

argument.required=Ebagum lad, the {0} argument is required, I say, required.

public static void main(final String[] args) {

MessageSource resources = new ClassPathXmlApplicationContext("beans.xml");

String message = resources.getMessage("argument.required",

new Object [] {"userDao"}, "Required", Locale.UK);

System.out.println(message);

}

The resulting output from the running of the above program will be…

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 128

Ebagum lad, the userDao argument is required, I say, required.

You can also use the MessageSourceAware interface to acquire a reference to any MessageSource

that has been defined. Any bean that is defined in an ApplicationContext that implements the

MessageSourceAware interface is injected with the application context’s MessageSource when the

bean is created and configured.

Note

As an alternative to ResourceBundleMessageSource, Spring provides a

ReloadableResourceBundleMessageSource class. This variant supports the same bundle

file format but is more flexible than the standard JDK based ResourceBundleMessageSource

implementation. In particular, it allows for reading files from any Spring resource location (not just

from the classpath) and supports hot reloading of bundle property files (while efficiently caching

them in between). Check out the ReloadableResourceBundleMessageSource javadocs for

details.

Standard and Custom Events

Event handling in the ApplicationContext is provided through the ApplicationEvent class

and ApplicationListener interface. If a bean that implements the ApplicationListener

interface is deployed into the context, every time an ApplicationEvent gets published to the

ApplicationContext, that bean is notified. Essentially, this is the standard Observer design pattern.

Spring provides the following standard events:

Table 5.7. Built-in Events

Event Explanation

ContextRefreshedEvent Published when the ApplicationContext

is initialized or refreshed, for example,

using the refresh() method on the

ConfigurableApplicationContext

interface. "Initialized" here means that all

beans are loaded, post-processor beans are

detected and activated, singletons are pre-

instantiated, and the ApplicationContext

object is ready for use. As long as the

context has not been closed, a refresh can

be triggered multiple times, provided that

the chosen ApplicationContext actually

supports such "hot" refreshes. For example,

XmlWebApplicationContext supports hot

refreshes, but GenericApplicationContext

does not.

ContextStartedEvent Published when the ApplicationContext

is started, using the start() method on

the ConfigurableApplicationContext

interface. "Started" here means that all

Lifecycle beans receive an explicit start

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 129

Event Explanation

signal. Typically this signal is used to restart

beans after an explicit stop, but it may also

be used to start components that have not

been configured for autostart , for example,

components that have not already started on

initialization.

ContextStoppedEvent Published when the ApplicationContext

is stopped, using the stop() method on

the ConfigurableApplicationContext

interface. "Stopped" here means that all

Lifecycle beans receive an explicit stop

signal. A stopped context may be restarted

through a start() call.

ContextClosedEvent Published when the ApplicationContext

is closed, using the close() method on the

ConfigurableApplicationContext

interface. "Closed" here means that all singleton

beans are destroyed. A closed context reaches

its end of life; it cannot be refreshed or restarted.

RequestHandledEvent A web-specific event telling all beans that an

HTTP request has been serviced. This event

is published after the request is complete. This

event is only applicable to web applications

using Spring’s DispatcherServlet.

You can also create and publish your own custom events. This example demonstrates a simple class

that extends Spring’s ApplicationEvent base class:

public class BlackListEvent extends ApplicationEvent {

private final String address;

private final String test;

public BlackListEvent(Object source, String address, String test) {

super(source);

this.address = address;

this.test = test;

}

// accessor and other methods...

}

To publish a custom ApplicationEvent, call the publishEvent() method on an

ApplicationEventPublisher. Typically this is done by creating a class that implements

ApplicationEventPublisherAware and registering it as a Spring bean. The following example

demonstrates such a class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 130

public class EmailService implements ApplicationEventPublisherAware {

private List<String> blackList;

private ApplicationEventPublisher publisher;

public void setBlackList(List<String> blackList) {

this.blackList = blackList;

}

public void setApplicationEventPublisher(ApplicationEventPublisher publisher) {

this.publisher = publisher;

}

public void sendEmail(String address, String text) {

if (blackList.contains(address)) {

BlackListEvent event = new BlackListEvent(this, address, text);

publisher.publishEvent(event);

return;

}

// send email...

}

At configuration time, the Spring container will detect that EmailService

implements ApplicationEventPublisherAware and will automatically call

setApplicationEventPublisher(). In reality, the parameter passed in will be the Spring container

itself; you’re simply interacting with the application context via its ApplicationEventPublisher

interface.

To receive the custom ApplicationEvent, create a class that implements ApplicationListener

and register it as a Spring bean. The following example demonstrates such a class:

public class BlackListNotifier implements ApplicationListener<BlackListEvent> {

private String notificationAddress;

public void setNotificationAddress(String notificationAddress) {

this.notificationAddress = notificationAddress;

}

public void onApplicationEvent(BlackListEvent event) {

// notify appropriate parties via notificationAddress...

}

Notice that ApplicationListener is generically parameterized with the type of your custom event,

BlackListEvent. This means that the onApplicationEvent() method can remain type-safe,

avoiding any need for downcasting. You may register as many event listeners as you wish, but note that

by default event listeners receive events synchronously. This means the publishEvent() method

blocks until all listeners have finished processing the event. One advantage of this synchronous and

single-threaded approach is that when a listener receives an event, it operates inside the transaction

context of the publisher if a transaction context is available. If another strategy for event publication

becomes necessary, refer to the JavaDoc for Spring’s ApplicationEventMulticaster interface.

The following example shows the bean definitions used to register and configure each of the classes

above:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 131

<list>

<value>known.spammer@example.org</value>

<value>known.hacker@example.org</value>

<value>john.doe@example.org</value>

</list>

</property>

</bean>

</bean>

Putting it all together, when the sendEmail() method of the emailService bean is called, if there

are any emails that should be blacklisted, a custom event of type BlackListEvent is published.

The blackListNotifier bean is registered as an ApplicationListener and thus receives the

BlackListEvent, at which point it can notify appropriate parties.

Note

Spring’s eventing mechanism is designed for simple communication between Spring beans within

the same application context. However, for more sophisticated enterprise integration needs,

the separately-maintained Spring Integration project provides complete support for building

lightweight, pattern-oriented, event-driven architectures that build upon the well-known Spring

programming model.

Convenient access to low-level resources

For optimal usage and understanding of application contexts, users should generally familiarize

themselves with Spring’s Resource abstraction, as described in the chapter Chapter 6, Resources.

An application context is a ResourceLoader, which can be used to load Resources. A Resource is

essentially a more feature rich version of the JDK class java.net.URL, in fact, the implementations

of the Resource wrap an instance of java.net.URL where appropriate. A Resource can obtain

low-level resources from almost any location in a transparent fashion, including from the classpath,

a filesystem location, anywhere describable with a standard URL, and some other variations. If the

resource location string is a simple path without any special prefixes, where those resources come from

is specific and appropriate to the actual application context type.

You can configure a bean deployed into the application context to implement the special callback

interface, ResourceLoaderAware, to be automatically called back at initialization time with the

application context itself passed in as the ResourceLoader. You can also expose properties of type

Resource, to be used to access static resources; they will be injected into it like any other properties.

You can specify those Resource properties as simple String paths, and rely on a special JavaBean

PropertyEditor that is automatically registered by the context, to convert those text strings to actual

Resource objects when the bean is deployed.

The location path or paths supplied to an ApplicationContext constructor are actually resource

strings, and in simple form are treated appropriately to the specific context implementation.

ClassPathXmlApplicationContext treats a simple location path as a classpath location. You can

also use location paths (resource strings) with special prefixes to force loading of definitions from the

classpath or a URL, regardless of the actual context type.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 132

Convenient ApplicationContext instantiation for web applications

You can create ApplicationContext instances declaratively by using, for example, a

ContextLoader. Of course you can also create ApplicationContext instances programmatically

by using one of the ApplicationContext implementations.

You can register an ApplicationContext using the ContextLoaderListener as follows:

<context-param>

<param-name>contextConfigLocation</param-name>

<param-value>/WEB-INF/daoContext.xml /WEB-INF/applicationContext.xml</param-value>

</context-param>

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

<!-- or use the ContextLoaderServlet instead of the above listener

<servlet-name>context</servlet-name>

<servlet-class>org.springframework.web.context.ContextLoaderServlet</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

-->

The listener inspects the contextConfigLocation parameter. If the parameter does not exist, the

listener uses /WEB-INF/applicationContext.xml as a default. When the parameter does exist,

the listener separates the String by using predefined delimiters (comma, semicolon and whitespace)

and uses the values as locations where application contexts will be searched. Ant-style path patterns

are supported as well. Examples are /WEB-INF/*Context.xml for all files with names ending with

"Context.xml", residing in the "WEB-INF" directory, and /WEB-INF/**/*Context.xml, for all such

files in any subdirectory of "WEB-INF".

You can use ContextLoaderServlet instead of ContextLoaderListener. The Servlet uses the

contextConfigLocation parameter just as the listener does.

Deploying a Spring ApplicationContext as a Java EE RAR file

It is possible to deploy a Spring ApplicationContext as a RAR file, encapsulating the context and all of

its required bean classes and library JARs in a Java EE RAR deployment unit. This is the equivalent

of bootstrapping a standalone ApplicationContext, just hosted in Java EE environment, being able

to access the Java EE servers facilities. RAR deployment is more natural alternative to scenario of

deploying a headless WAR file, in effect, a WAR file without any HTTP entry points that is used only for

bootstrapping a Spring ApplicationContext in a Java EE environment.

RAR deployment is ideal for application contexts that do not need HTTP entry points but rather

consist only of message endpoints and scheduled jobs. Beans in such a context can use application

server resources such as the JTA transaction manager and JNDI-bound JDBC DataSources and JMS

ConnectionFactory instances, and may also register with the platform’s JMX server - all through Spring’s

standard transaction management and JNDI and JMX support facilities. Application components

can also interact with the application server’s JCA WorkManager through Spring’s TaskExecutor

abstraction.

Check out the JavaDoc of the SpringContextResourceAdapter class for the configuration details

involved in RAR deployment.

For a simple deployment of a Spring ApplicationContext as a Java EE RAR file: package all application

classes into a RAR file, which is a standard JAR file with a different file extension. Add all required

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 133

library JARs into the root of the RAR archive. Add a "META-INF/ra.xml" deployment descriptor (as

shown in SpringContextResourceAdapter's JavaDoc) and the corresponding Spring XML bean

definition file(s) (typically "META-INF/applicationContext.xml"), and drop the resulting RAR file into your

application server’s deployment directory.

Note

Such RAR deployment units are usually self-contained; they do not expose components to the

outside world, not even to other modules of the same application. Interaction with a RAR-based

ApplicationContext usually occurs through JMS destinations that it shares with other modules. A

RAR-based ApplicationContext may also, for example, schedule some jobs, reacting to new files

in the file system (or the like). If it needs to allow synchronous access from the outside, it could

for example export RMI endpoints, which of course may be used by other application modules

on the same machine.

5.16 The BeanFactory

The BeanFactory provides the underlying basis for Spring’s IoC functionality but it is only used

directly in integration with other third-party frameworks and is now largely historical in nature for

most users of Spring. The BeanFactory and related interfaces, such as BeanFactoryAware,

InitializingBean, DisposableBean, are still present in Spring for the purposes of backward

compatibility with the large number of third-party frameworks that integrate with Spring. Often third-party

components that can not use more modern equivalents such as @PostConstruct or @PreDestroy

in order to remain compatible with JDK 1.4 or to avoid a dependency on JSR-250.

This section provides additional background into the differences between the BeanFactory and

ApplicationContext and how one might access the IoC container directly through a classic singleton

lookup.

BeanFactory or ApplicationContext?

Use an ApplicationContext unless you have a good reason for not doing so.

Because the ApplicationContext includes all functionality of the BeanFactory, it is generally

recommended over the BeanFactory, except for a few situations such as in an Applet where memory

consumption might be critical and a few extra kilobytes might make a difference. However, for most

typical enterprise applications and systems, the ApplicationContext is what you will want to use.

Spring makes heavy use of the BeanPostProcessor extension point (to effect proxying and so on). If

you use only a plain BeanFactory, a fair amount of support such as transactions and AOP will not take

effect, at least not without some extra steps on your part. This situation could be confusing because

nothing is actually wrong with the configuration.

The following table lists features provided by the BeanFactory and ApplicationContext interfaces

and implementations.

Table 5.8. Feature Matrix

Feature BeanFactory ApplicationContext

Bean instantiation/wiring Yes Yes

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 134

Feature BeanFactory ApplicationContext

Automatic

BeanPostProcessor

registration

No Yes

Automatic

BeanFactoryPostProcessor

registration

No Yes

Convenient MessageSource

access (for i18n)

No Yes

ApplicationEvent

publication

No Yes

To explicitly register a bean post-processor with a BeanFactory implementation, you must write code

like this:

ConfigurableBeanFactory factory = new XmlBeanFactory(...);

// now register any needed BeanPostProcessor instances

MyBeanPostProcessor postProcessor = new MyBeanPostProcessor();

factory.addBeanPostProcessor(postProcessor);

// now start using the factory

To explicitly register a BeanFactoryPostProcessor when using a BeanFactory implementation,

you must write code like this:

XmlBeanFactory factory = new XmlBeanFactory(new FileSystemResource("beans.xml"));

// bring in some property values from a Properties file

PropertyPlaceholderConfigurer cfg = new PropertyPlaceholderConfigurer();

cfg.setLocation(new FileSystemResource("jdbc.properties"));

// now actually do the replacement

cfg.postProcessBeanFactory(factory);

In both cases, the explicit registration step is inconvenient, which is one reason why

the various ApplicationContext implementations are preferred above plain BeanFactory

implementations in the vast majority of Spring-backed applications, especially when using

BeanFactoryPostProcessors and BeanPostProcessors. These mechanisms implement

important functionality such as property placeholder replacement and AOP.

Glue code and the evil singleton

It is best to write most application code in a dependency-injection (DI) style, where that code is served

out of a Spring IoC container, has its own dependencies supplied by the container when it is created, and

is completely unaware of the container. However, for the small glue layers of code that are sometimes

needed to tie other code together, you sometimes need a singleton (or quasi-singleton) style access

to a Spring IoC container. For example, third-party code may try to construct new objects directly (

Class.forName() style), without the ability to get these objects out of a Spring IoC container.If the

object constructed by the third-party code is a small stub or proxy, which then uses a singleton style

access to a Spring IoC container to get a real object to delegate to, then inversion of control has still been

achieved for the majority of the code (the object coming out of the container). Thus most code is still

unaware of the container or how it is accessed, and remains decoupled from other code, with all ensuing

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 135

benefits. EJBs may also use this stub/proxy approach to delegate to a plain Java implementation object,

retrieved from a Spring IoC container. While the Spring IoC container itself ideally does not have to be

a singleton, it may be unrealistic in terms of memory usage or initialization times (when using beans in

the Spring IoC container such as a Hibernate SessionFactory) for each bean to use its own, non-

singleton Spring IoC container.

Looking up the application context in a service locator style is sometimes the only option for accessing

shared Spring-managed components, such as in an EJB 2.1 environment, or when you want to share

a single ApplicationContext as a parent to WebApplicationContexts across WAR files. In this case

you should look into using the utility class ContextSingletonBeanFactoryLocator locator that is

described in this Spring team blog entry.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 136

6. Resources

6.1 Introduction

Java’s standard java.net.URL class and standard handlers for various URL prefixes unfortunately are

not quite adequate enough for all access to low-level resources. For example, there is no standardized

URL implementation that may be used to access a resource that needs to be obtained from the classpath,

or relative to a ServletContext. While it is possible to register new handlers for specialized URL

prefixes (similar to existing handlers for prefixes such as http:), this is generally quite complicated, and

the URL interface still lacks some desirable functionality, such as a method to check for the existence

of the resource being pointed to.

6.2 The Resource interface

Spring’s Resource interface is meant to be a more capable interface for abstracting access to low-

level resources.

public interface Resource extends InputStreamSource {

boolean exists();

boolean isOpen();

URL getURL() throws IOException;

File getFile() throws IOException;

Resource createRelative(String relativePath) throws IOException;

String getFilename();

String getDescription();

}

public interface InputStreamSource {

InputStream getInputStream() throws IOException;

}

Some of the most important methods from the Resource interface are:

•getInputStream(): locates and opens the resource, returning an InputStream for reading from

the resource. It is expected that each invocation returns a fresh InputStream. It is the responsibility

of the caller to close the stream.

•exists(): returns a boolean indicating whether this resource actually exists in physical form.

•isOpen(): returns a boolean indicating whether this resource represents a handle with an open

stream. If true, the InputStream cannot be read multiple times, and must be read once only and

then closed to avoid resource leaks. Will be false for all usual resource implementations, with the

exception of InputStreamResource.

•getDescription(): returns a description for this resource, to be used for error output when working

with the resource. This is often the fully qualified file name or the actual URL of the resource.

Other methods allow you to obtain an actual URL or File object representing the resource (if the

underlying implementation is compatible, and supports that functionality).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 137

The Resource abstraction is used extensively in Spring itself, as an argument type in many method

signatures when a resource is needed. Other methods in some Spring APIs (such as the constructors to

various ApplicationContext implementations), take a String which in unadorned or simple form

is used to create a Resource appropriate to that context implementation, or via special prefixes on

the String path, allow the caller to specify that a specific Resource implementation must be created

and used.

While the Resource interface is used a lot with Spring and by Spring, it’s actually very useful to use as

a general utility class by itself in your own code, for access to resources, even when your code doesn’t

know or care about any other parts of Spring. While this couples your code to Spring, it really only

couples it to this small set of utility classes, which are serving as a more capable replacement for URL,

and can be considered equivalent to any other library you would use for this purpose.

It is important to note that the Resource abstraction does not replace functionality: it wraps it where

possible. For example, a UrlResource wraps a URL, and uses the wrapped URL to do its work.

6.3 Built-in Resource implementations

There are a number of Resource implementations that come supplied straight out of the box in Spring:

UrlResource

The UrlResource wraps a java.net.URL, and may be used to access any object that is normally

accessible via a URL, such as files, an HTTP target, an FTP target, etc. All URLs have a standardized

String representation, such that appropriate standardized prefixes are used to indicate one URL type

from another. This includes file: for accessing filesystem paths, http: for accessing resources via

the HTTP protocol, ftp: for accessing resources via FTP, etc.

A UrlResource is created by Java code explicitly using the UrlResource constructor, but will often

be created implicitly when you call an API method which takes a String argument which is meant

to represent a path. For the latter case, a JavaBeans PropertyEditor will ultimately decide which

type of Resource to create. If the path string contains a few well-known (to it, that is) prefixes such as

classpath:, it will create an appropriate specialized Resource for that prefix. However, if it doesn’t

recognize the prefix, it will assume the this is just a standard URL string, and will create a UrlResource.

ClassPathResource

This class represents a resource which should be obtained from the classpath. This uses either the

thread context class loader, a given class loader, or a given class for loading resources.

This Resource implementation supports resolution as java.io.File if the class path resource

resides in the file system, but not for classpath resources which reside in a jar and have not been

expanded (by the servlet engine, or whatever the environment is) to the filesystem. To address this the

various Resource implementations always support resolution as a java.net.URL.

A ClassPathResource is created by Java code explicitly using the ClassPathResource

constructor, but will often be created implicitly when you call an API method which takes a String

argument which is meant to represent a path. For the latter case, a JavaBeans PropertyEditor will

recognize the special prefix classpath: on the string path, and create a ClassPathResource in

that case.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 138

FileSystemResource

This is a Resource implementation for java.io.File handles. It obviously supports resolution as a

File, and as a URL.

ServletContextResource

This is a Resource implementation for ServletContext resources, interpreting relative paths within

the relevant web application’s root directory.

This always supports stream access and URL access, but only allows java.io.File access when

the web application archive is expanded and the resource is physically on the filesystem. Whether or

not it’s expanded and on the filesystem like this, or accessed directly from the JAR or somewhere else

like a DB (it’s conceivable) is actually dependent on the Servlet container.

InputStreamResource

A Resource implementation for a given InputStream. This should only be used if no specific

Resource implementation is applicable. In particular, prefer ByteArrayResource or any of the file-

based Resource implementations where possible.

In contrast to other Resource implementations, this is a descriptor for an already opened resource -

therefore returning true from isOpen(). Do not use it if you need to keep the resource descriptor

somewhere, or if you need to read a stream multiple times.

ByteArrayResource

This is a Resource implementation for a given byte array. It creates a ByteArrayInputStream for

the given byte array.

It’s useful for loading content from any given byte array, without having to resort to a single-use

InputStreamResource.

6.4 The ResourceLoader

The ResourceLoader interface is meant to be implemented by objects that can return (i.e. load)

Resource instances.

public interface ResourceLoader {

Resource getResource(String location);

}

All application contexts implement the ResourceLoader interface, and therefore all application

contexts may be used to obtain Resource instances.

When you call getResource() on a specific application context, and the location path specified

doesn’t have a specific prefix, you will get back a Resource type that is appropriate to that particular

application context. For example, assume the following snippet of code was executed against a

ClassPathXmlApplicationContext instance:

Resource template = ctx.getResource("some/resource/path/myTemplate.txt");

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 139

What would be returned would be a ClassPathResource; if the same method was executed against

a FileSystemXmlApplicationContext instance, you’d get back a FileSystemResource. For a

WebApplicationContext, you’d get back a ServletContextResource, and so on.

As such, you can load resources in a fashion appropriate to the particular application context.

On the other hand, you may also force ClassPathResource to be used, regardless of the application

context type, by specifying the special classpath: prefix:

Resource template = ctx.getResource("classpath:some/resource/path/myTemplate.txt");

Similarly, one can force a UrlResource to be used by specifying any of the standard java.net.URL

prefixes:

Resource template = ctx.getResource("file:/some/resource/path/myTemplate.txt");

Resource template = ctx.getResource("http://myhost.com/resource/path/myTemplate.txt");

The following table summarizes the strategy for converting Strings to Resources:

Table 6.1. Resource strings

Prefix Example Explanation

classpath: classpath:com/myapp/

config.xml

Loaded from the classpath.

file: file:/data/config.xml Loaded as a URL, from the

filesystem. 1

http: http://myserver/

logo.png

Loaded as a URL.

(none) /data/config.xml Depends on the underlying

ApplicationContext.

1But see also the section called “FileSystemResource caveats”.

6.5 The ResourceLoaderAware interface

The ResourceLoaderAware interface is a special marker interface, identifying objects that expect to

be provided with a ResourceLoader reference.

public interface ResourceLoaderAware {

void setResourceLoader(ResourceLoader resourceLoader);

}

When a class implements ResourceLoaderAware and is deployed into an application context (as a

Spring-managed bean), it is recognized as ResourceLoaderAware by the application context. The

application context will then invoke the setResourceLoader(ResourceLoader), supplying itself as

the argument (remember, all application contexts in Spring implement the ResourceLoader interface).

Of course, since an ApplicationContext is a ResourceLoader, the bean could also implement

the ApplicationContextAware interface and use the supplied application context directly to load

resources, but in general, it’s better to use the specialized ResourceLoader interface if that’s all that’s

needed. The code would just be coupled to the resource loading interface, which can be considered a

utility interface, and not the whole Spring ApplicationContext interface.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 140

As of Spring 2.5, you can rely upon autowiring of the ResourceLoader as an alternative to

implementing the ResourceLoaderAware interface. The "traditional" constructor and byType

autowiring modes (as described in the section called “Autowiring collaborators”) are now capable

of providing a dependency of type ResourceLoader for either a constructor argument or setter

method parameter respectively. For more flexibility (including the ability to autowire fields and multiple

parameter methods), consider using the new annotation-based autowiring features. In that case, the

ResourceLoader will be autowired into a field, constructor argument, or method parameter that is

expecting the ResourceLoader type as long as the field, constructor, or method in question carries

the @Autowired annotation. For more information, see the section called “@Autowired”.

6.6 Resources as dependencies

If the bean itself is going to determine and supply the resource path through some sort of dynamic

process, it probably makes sense for the bean to use the ResourceLoader interface to load resources.

Consider as an example the loading of a template of some sort, where the specific resource that is

needed depends on the role of the user. If the resources are static, it makes sense to eliminate the use

of the ResourceLoader interface completely, and just have the bean expose the Resource properties

it needs, and expect that they will be injected into it.

What makes it trivial to then inject these properties, is that all application contexts register and use a

special JavaBeans PropertyEditor which can convert String paths to Resource objects. So if

myBean has a template property of type Resource, it can be configured with a simple string for that

resource, as follows:

</bean>

Note that the resource path has no prefix, so because the application context itself is going to

be used as the ResourceLoader, the resource itself will be loaded via a ClassPathResource,

FileSystemResource, or ServletContextResource (as appropriate) depending on the exact type

of the context.

If there is a need to force a specific Resource type to be used, then a prefix may be used. The following

two examples show how to force a ClassPathResource and a UrlResource (the latter being used

to access a filesystem file).

6.7 Application contexts and Resource paths

Constructing application contexts

An application context constructor (for a specific application context type) generally takes a string or

array of strings as the location path(s) of the resource(s) such as XML files that make up the definition

of the context.

When such a location path doesn’t have a prefix, the specific Resource type built from that path and

used to load the bean definitions, depends on and is appropriate to the specific application context. For

example, if you create a ClassPathXmlApplicationContext as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 141

ApplicationContext ctx = new ClassPathXmlApplicationContext("conf/appContext.xml");

The bean definitions will be loaded from the classpath, as a ClassPathResource will be used. But if

you create a FileSystemXmlApplicationContext as follows:

ApplicationContext ctx =

new FileSystemXmlApplicationContext("conf/appContext.xml");

The bean definition will be loaded from a filesystem location, in this case relative to the current working

directory.

Note that the use of the special classpath prefix or a standard URL prefix on the location

path will override the default type of Resource created to load the definition. So this

FileSystemXmlApplicationContext…

ApplicationContext ctx =

new FileSystemXmlApplicationContext("classpath:conf/appContext.xml");

i. will actually load its bean definitions from the classpath. However, it is still a

FileSystemXmlApplicationContext. If it is subsequently used as a ResourceLoader, any

unprefixed paths will still be treated as filesystem paths.

Constructing ClassPathXmlApplicationContext instances - shortcuts

The ClassPathXmlApplicationContext exposes a number of constructors to enable convenient

instantiation. The basic idea is that one supplies merely a string array containing just the filenames of

the XML files themselves (without the leading path information), and one also supplies a Class; the

ClassPathXmlApplicationContext will derive the path information from the supplied class.

An example will hopefully make this clear. Consider a directory layout that looks like this:

com/

foo/

services.xml

daos.xml

MessengerService.class

A ClassPathXmlApplicationContext instance composed of the beans defined in the

'services.xml' and 'daos.xml' could be instantiated like so…

ApplicationContext ctx = new ClassPathXmlApplicationContext(

new String[] {"services.xml", "daos.xml"}, MessengerService.class);

Please do consult the ClassPathXmlApplicationContext javadocs for details on the various

constructors.

Wildcards in application context constructor resource paths

The resource paths in application context constructor values may be a simple path (as shown

above) which has a one-to-one mapping to a target Resource, or alternately may contain the special

"classpath*:" prefix and/or internal Ant-style regular expressions (matched using Spring’s PathMatcher

utility). Both of the latter are effectively wildcards

One use for this mechanism is when doing component-style application assembly. All components can

publish context definition fragments to a well-known location path, and when the final application context

is created using the same path prefixed via classpath*:, all component fragments will be picked up

automatically.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 142

Note that this wildcarding is specific to use of resource paths in application context constructors (or

when using the PathMatcher utility class hierarchy directly), and is resolved at construction time. It

has nothing to do with the Resource type itself. It’s not possible to use the classpath*: prefix to

construct an actual Resource, as a resource points to just one resource at a time.

Ant-style Patterns

When the path location contains an Ant-style pattern, for example:

/WEB-INF/-context.xml

com/mycompany//applicationContext.xml

file:C:/some/path/-context.xml

classpath:com/mycompany//applicationContext.xml

i. the resolver follows a more complex but defined procedure to try to resolve the wildcard. It produces

a Resource for the path up to the last non-wildcard segment and obtains a URL from it. If this URL

is not a "jar:" URL or container-specific variant (e.g. " zip:" in WebLogic, " wsjar" in WebSphere,

etc.), then a java.io.File is obtained from it and used to resolve the wildcard by traversing the

filesystem. In the case of a jar URL, the resolver either gets a java.net.JarURLConnection from

it or manually parses the jar URL and then traverses the contents of the jar file to resolve the wildcards.

Implications on portability

If the specified path is already a file URL (either explicitly, or implicitly because the base

ResourceLoader is a filesystem one, then wildcarding is guaranteed to work in a completely portable

fashion.

If the specified path is a classpath location, then the resolver must obtain the last non-wildcard path

segment URL via a Classloader.getResource() call. Since this is just a node of the path (not the

file at the end) it is actually undefined (in the ClassLoader javadocs) exactly what sort of a URL is

returned in this case. In practice, it is always a java.io.File representing the directory, where the

classpath resource resolves to a filesystem location, or a jar URL of some sort, where the classpath

resource resolves to a jar location. Still, there is a portability concern on this operation.

If a jar URL is obtained for the last non-wildcard segment, the resolver must be able to get a

java.net.JarURLConnection from it, or manually parse the jar URL, to be able to walk the contents

of the jar, and resolve the wildcard. This will work in most environments, but will fail in others, and it is

strongly recommended that the wildcard resolution of resources coming from jars be thoroughly tested

in your specific environment before you rely on it.

The Classpath*: portability classpath*: prefix

When constructing an XML-based application context, a location string may use the special

classpath*: prefix:

ApplicationContext ctx =

new ClassPathXmlApplicationContext("classpath*:conf/appContext.xml");

This special prefix specifies that all classpath resources that match the given name must be obtained

(internally, this essentially happens via a ClassLoader.getResources(...) call), and then merged

to form the final application context definition.

Note

The wildcard classpath relies on the getResources() method of the underlying classloader.

As most application servers nowadays supply their own classloader implementation, the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 143

behavior might differ especially when dealing with jar files. A simple test to check if

classpath* works is to use the classloader to load a file from within a jar on the classpath:

getClass().getClassLoader().getResources("<someFileInsideTheJar>"). Try

this test with files that have the same name but are placed inside two different locations. In case

an inappropriate result is returned, check the application server documentation for settings that

might affect the classloader behavior.

The " classpath*:" prefix can also be combined with a PathMatcher pattern in the rest of the location

path, for example " classpath*:META-INF/*-beans.xml". In this case, the resolution strategy is

fairly simple: a ClassLoader.getResources() call is used on the last non-wildcard path segment to get all

the matching resources in the class loader hierarchy, and then off each resource the same PathMatcher

resolution strategy described above is used for the wildcard subpath.

Other notes relating to wildcards

Please note that " classpath*:" when combined with Ant-style patterns will only work reliably with at

least one root directory before the pattern starts, unless the actual target files reside in the file system.

This means that a pattern like " classpath*:*.xml" will not retrieve files from the root of jar files

but rather only from the root of expanded directories. This originates from a limitation in the JDK’s

ClassLoader.getResources() method which only returns file system locations for a passed-in

empty string (indicating potential roots to search).

Ant-style patterns with " classpath:" resources are not guaranteed to find matching resources if the

root package to search is available in multiple class path locations. This is because a resource such as

com/mycompany/package1/service-context.xml

may be in only one location, but when a path such as

classpath:com/mycompany/**/service-context.xml

is used to try to resolve it, the resolver will work off the (first) URL returned by getResource("com/

mycompany");. If this base package node exists in multiple classloader locations, the actual end

resource may not be underneath. Therefore, preferably, use " classpath*:" with the same Ant-style

pattern in such a case, which will search all class path locations that contain the root package.

FileSystemResource caveats

A FileSystemResource that is not attached to a FileSystemApplicationContext (that is,

a FileSystemApplicationContext is not the actual ResourceLoader) will treat absolute vs.

relative paths as you would expect. Relative paths are relative to the current working directory, while

absolute paths are relative to the root of the filesystem.

For backwards compatibility (historical) reasons however, this changes

when the FileSystemApplicationContext is the ResourceLoader. The

FileSystemApplicationContext simply forces all attached FileSystemResource instances to

treat all location paths as relative, whether they start with a leading slash or not. In practice, this means

the following are equivalent:

ApplicationContext ctx =

new FileSystemXmlApplicationContext("conf/context.xml");

ApplicationContext ctx =

new FileSystemXmlApplicationContext("/conf/context.xml");

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 144

As are the following: (Even though it would make sense for them to be different, as one case is relative

and the other absolute.)

FileSystemXmlApplicationContext ctx = ...;

ctx.getResource("some/resource/path/myTemplate.txt");

FileSystemXmlApplicationContext ctx = ...;

ctx.getResource("/some/resource/path/myTemplate.txt");

In practice, if true absolute filesystem paths are needed, it is better to forgo the use of absolute paths

with FileSystemResource / FileSystemXmlApplicationContext, and just force the use of a

UrlResource, by using the file: URL prefix.

// actual context type doesn't matter, the Resource will always be UrlResource

ctx.getResource("file:/some/resource/path/myTemplate.txt");

// force this FileSystemXmlApplicationContext to load its definition via a UrlResource

ApplicationContext ctx =

new FileSystemXmlApplicationContext("file:/conf/context.xml");

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 145

7. Validation, Data Binding, and Type Conversion

7.1 Introduction

JSR-303/JSR-349 Bean Validation

Spring Framework 4.0 supports Bean Validation 1.0 (JSR-303) and Bean Validation 1.1 (JSR-349)

in terms of setup support, also adapting it to Spring’s Validator interface.

An application can choose to enable Bean Validation once globally, as described in Section 7.8,

“Spring Validation”, and use it exclusively for all validation needs.

An application can also register additional Spring Validator instances per DataBinder

instance, as described in the section called “Configuring a DataBinder”. This may be useful for

plugging in validation logic without the use of annotations.

There are pros and cons for considering validation as business logic, and Spring offers a design for

validation (and data binding) that does not exclude either one of them. Specifically validation should

not be tied to the web tier, should be easy to localize and it should be possible to plug in any validator

available. Considering the above, Spring has come up with a Validator interface that is both basic

ands eminently usable in every layer of an application.

Data binding is useful for allowing user input to be dynamically bound to the domain model of

an application (or whatever objects you use to process user input). Spring provides the so-called

DataBinder to do exactly that. The Validator and the DataBinder make up the validation

package, which is primarily used in but not limited to the MVC framework.

The BeanWrapper is a fundamental concept in the Spring Framework and is used in a lot of places.

However, you probably will not have the need to use the BeanWrapper directly. Because this is

reference documentation however, we felt that some explanation might be in order. We will explain the

BeanWrapper in this chapter since, if you were going to use it at all, you would most likely do so when

trying to bind data to objects.

Spring’s DataBinder and the lower-level BeanWrapper both use PropertyEditors to parse and format

property values. The PropertyEditor concept is part of the JavaBeans specification, and is also

explained in this chapter. Spring 3 introduces a "core.convert" package that provides a general type

conversion facility, as well as a higher-level "format" package for formatting UI field values. These new

packages may be used as simpler alternatives to PropertyEditors, and will also be discussed in this

chapter.

7.2 Validation using Spring’s Validator interface

Spring features a Validator interface that you can use to validate objects. The Validator interface

works using an Errors object so that while validating, validators can report validation failures to the

Errors object.

Let’s consider a small data object:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 146

public class Person {

private String name;

private int age;

// the usual getters and setters...

}

We’re going to provide validation behavior for the Person class by implementing the following two

methods of the org.springframework.validation.Validator interface:

•supports(Class) - Can this Validator validate instances of the supplied Class?

•validate(Object, org.springframework.validation.Errors) - validates the given

object and in case of validation errors, registers those with the given Errors object

Implementing a Validator is fairly straightforward, especially when you know of the

ValidationUtils helper class that the Spring Framework also provides.

public class PersonValidator implements Validator {

* This Validator validates *just Person instances

public boolean supports(Class clazz) {

return Person.class.equals(clazz);

}

public void validate(Object obj, Errors e) {

ValidationUtils.rejectIfEmpty(e, "name", "name.empty");

Person p = (Person) obj;

if (p.getAge() < 0) {

e.rejectValue("age", "negativevalue");

} else if (p.getAge() > 110) {

e.rejectValue("age", "too.darn.old");

}

As you can see, the static rejectIfEmpty(..) method on the ValidationUtils class is used

to reject the 'name' property if it is null or the empty string. Have a look at the ValidationUtils

javadocs to see what functionality it provides besides the example shown previously.

While it is certainly possible to implement a single Validator class to validate each of the nested

objects in a rich object, it may be better to encapsulate the validation logic for each nested class

of object in its own Validator implementation. A simple example of a 'rich' object would be a

Customer that is composed of two String properties (a first and second name) and a complex

Address object. Address objects may be used independently of Customer objects, and so a distinct

AddressValidator has been implemented. If you want your CustomerValidator to reuse the

logic contained within the AddressValidator class without resorting to copy-and-paste, you can

dependency-inject or instantiate an AddressValidator within your CustomerValidator, and use

it like so:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 147

public class CustomerValidator implements Validator {

private final Validator addressValidator;

public CustomerValidator(Validator addressValidator) {

if (addressValidator == null) {

throw new IllegalArgumentException("The supplied [Validator] is " +

"required and must not be null.");

}

if (!addressValidator.supports(Address.class)) {

throw new IllegalArgumentException("The supplied [Validator] must " +

support the validation of [Address] instances.");

}

this.addressValidator = addressValidator;

}

/**

* This Validator validates Customer instances, and any subclasses of Customer too

public boolean supports(Class clazz) {

return Customer.class.isAssignableFrom(clazz);

}

public void validate(Object target, Errors errors) {

ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "field.required");

ValidationUtils.rejectIfEmptyOrWhitespace(errors, "surname", "field.required");

Customer customer = (Customer) target;

try {

errors.pushNestedPath("address");

ValidationUtils.invokeValidator(this.addressValidator, customer.getAddress(), errors);

} finally {

errors.popNestedPath();

}

Validation errors are reported to the Errors object passed to the validator. In case of Spring Web MVC

you can use <spring:bind/> tag to inspect the error messages, but of course you can also inspect

the errors object yourself. More information about the methods it offers can be found in the javadocs.

7.3 Resolving codes to error messages

We’ve talked about databinding and validation. Outputting messages corresponding to validation errors

is the last thing we need to discuss. In the example we’ve shown above, we rejected the name and

the age field. If we’re going to output the error messages by using a MessageSource, we will do

so using the error code we’ve given when rejecting the field (name and age in this case). When

you call (either directly, or indirectly, using for example the ValidationUtils class) rejectValue

or one of the other reject methods from the Errors interface, the underlying implementation will

not only register the code you’ve passed in, but also a number of additional error codes. What

error codes it registers is determined by the MessageCodesResolver that is used. By default, the

DefaultMessageCodesResolver is used, which for example not only registers a message with

the code you gave, but also messages that include the field name you passed to the reject method.

So in case you reject a field using rejectValue("age", "too.darn.old"), apart from the

too.darn.old code, Spring will also register too.darn.old.age and too.darn.old.age.int

(so the first will include the field name and the second will include the type of the field); this is done as

a convenience to aid developers in targeting error messages and suchlike.

More information on the MessageCodesResolver and the default strategy can be found online in the

javadocs of MessageCodesResolver and DefaultMessageCodesResolver, respectively.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 148

7.4 Bean manipulation and the BeanWrapper

The org.springframework.beans package adheres to the JavaBeans standard provided by

Oracle. A JavaBean is simply a class with a default no-argument constructor, which follows a naming

convention where (by way of an example) a property named bingoMadness would have a setter

method setBingoMadness(..) and a getter method getBingoMadness(). For more information

about JavaBeans and the specification, please refer to Oracle’s website ( javabeans).

One quite important class in the beans package is the BeanWrapper interface and its corresponding

implementation ( BeanWrapperImpl). As quoted from the javadocs, the BeanWrapper offers

functionality to set and get property values (individually or in bulk), get property descriptors, and to

query properties to determine if they are readable or writable. Also, the BeanWrapper offers support

for nested properties, enabling the setting of properties on sub-properties to an unlimited depth. Then,

the BeanWrapper supports the ability to add standard JavaBeans PropertyChangeListeners and

VetoableChangeListeners, without the need for supporting code in the target class. Last but not

least, the BeanWrapper provides support for the setting of indexed properties. The BeanWrapper

usually isn’t used by application code directly, but by the DataBinder and the BeanFactory.

The way the BeanWrapper works is partly indicated by its name: it wraps a bean to perform actions

on that bean, like setting and retrieving properties.

Setting and getting basic and nested properties

Setting and getting properties is done using the setPropertyValue(s) and

getPropertyValue(s) methods that both come with a couple of overloaded variants. They’re all

described in more detail in the javadocs Spring comes with. What’s important to know is that there are

a couple of conventions for indicating properties of an object. A couple of examples:

Table 7.1. Examples of properties

Expression Explanation

name Indicates the property name corresponding to

the methods getName() or isName() and

setName(..)

account.name Indicates the nested property name of the

property account corresponding e.g. to the

methods getAccount().setName() or

getAccount().getName()

account[2] Indicates the third element of the indexed

property account. Indexed properties can be

of type array, list or other naturally ordered

collection

account[COMPANYNAME] Indicates the value of the map entry indexed by

the key COMPANYNAME of the Map property

account

Below you’ll find some examples of working with the BeanWrapper to get and set properties.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 149

(This next section is not vitally important to you if you’re not planning to work with the BeanWrapper

directly. If you’re just using the DataBinder and the BeanFactory and their out-of-the-box

implementation, you should skip ahead to the section about PropertyEditors.)

Consider the following two classes:

public class Company {

private String name;

private Employee managingDirector;

public String getName() {

return this.name;

}

public void setName(String name) {

this.name = name;

}

public Employee getManagingDirector() {

return this.managingDirector;

}

public void setManagingDirector(Employee managingDirector) {

this.managingDirector = managingDirector;

}

public class Employee {

private String name;

private float salary;

public String getName() {

return this.name;

}

public void setName(String name) {

this.name = name;

}

public float getSalary() {

return salary;

}

public void setSalary(float salary) {

this.salary = salary;

}

The following code snippets show some examples of how to retrieve and manipulate some of the

properties of instantiated Companies and Employees:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 150

BeanWrapper company = BeanWrapperImpl(new Company());

// setting the company name..

company.setPropertyValue("name", "Some Company Inc.");

// ... can also be done like this:

PropertyValue value = new PropertyValue("name", "Some Company Inc.");

company.setPropertyValue(value);

// ok, let's create the director and tie it to the company:

BeanWrapper jim = BeanWrapperImpl(new Employee());

jim.setPropertyValue("name", "Jim Stravinsky");

company.setPropertyValue("managingDirector", jim.getWrappedInstance());

// retrieving the salary of the managingDirector through the company

Float salary = (Float) company.getPropertyValue("managingDirector.salary");

Built-in PropertyEditor implementations

Spring uses the concept of PropertyEditors to effect the conversion between an Object and a

String. If you think about it, it sometimes might be handy to be able to represent properties in a

different way than the object itself. For example, a Date can be represented in a human readable way

(as the String ' 2007-14-09'), while we’re still able to convert the human readable form back to the

original date (or even better: convert any date entered in a human readable form, back to Date objects).

This behavior can be achieved by registering custom editors, of type java.beans.PropertyEditor.

Registering custom editors on a BeanWrapper or alternately in a specific IoC container as mentioned

in the previous chapter, gives it the knowledge of how to convert properties to the desired type. Read

more about PropertyEditors in the javadocs of the java.beans package provided by Oracle.

A couple of examples where property editing is used in Spring:

•setting properties on beans is done using PropertyEditors. When mentioning

java.lang.String as the value of a property of some bean you’re declaring in XML file, Spring

will (if the setter of the corresponding property has a Class-parameter) use the ClassEditor to try

to resolve the parameter to a Class object.

•parsing HTTP request parameters in Spring’s MVC framework is done using all kinds of

PropertyEditors that you can manually bind in all subclasses of the CommandController.

Spring has a number of built-in PropertyEditors to make life easy. Each of those is listed below

and they are all located in the org.springframework.beans.propertyeditors package. Most,

but not all (as indicated below), are registered by default by BeanWrapperImpl. Where the property

editor is configurable in some fashion, you can of course still register your own variant to override the

default one:

Table 7.2. Built-in PropertyEditors

Class Explanation

ByteArrayPropertyEditor Editor for byte arrays. Strings will simply

be converted to their corresponding byte

representations. Registered by default by

BeanWrapperImpl.

ClassEditor Parses Strings representing classes to actual

classes and the other way around. When a class

is not found, an IllegalArgumentException

is thrown. Registered by default by

BeanWrapperImpl.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 151

Class Explanation

CustomBooleanEditor Customizable property editor for Boolean

properties. Registered by default by

BeanWrapperImpl, but, can be overridden

by registering custom instance of it as custom

editor.

CustomCollectionEditor Property editor for Collections, converting

any source Collection to a given target

Collection type.

CustomDateEditor Customizable property editor for java.util.Date,

supporting a custom DateFormat. NOT

registered by default. Must be user registered as

needed with appropriate format.

CustomNumberEditor Customizable property editor for any Number

subclass like Integer, Long, Float, Double.

Registered by default by BeanWrapperImpl,

but can be overridden by registering custom

instance of it as a custom editor.

FileEditor Capable of resolving Strings to java.io.File

objects. Registered by default by

BeanWrapperImpl.

InputStreamEditor One-way property editor, capable of taking a

text string and producing (via an intermediate

ResourceEditor and Resource) an

InputStream, so InputStream properties

may be directly set as Strings. Note

that the default usage will not close the

InputStream for you! Registered by default by

BeanWrapperImpl.

LocaleEditor Capable of resolving Strings to Locale

objects and vice versa (the String format is

[country][variant], which is the same thing

the toString() method of Locale provides).

Registered by default by BeanWrapperImpl.

PatternEditor Capable of resolving Strings to

java.util.regex.Pattern objects and vice

versa.

PropertiesEditor Capable of converting Strings (formatted

using the format as defined in the javadocs

of the java.util.Properties class) to

Properties objects. Registered by default by

BeanWrapperImpl.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 152

Class Explanation

StringTrimmerEditor Property editor that trims Strings. Optionally

allows transforming an empty string into a null

value. NOT registered by default; must be user

registered as needed.

URLEditor Capable of resolving a String representation of

a URL to an actual URL object. Registered by

default by BeanWrapperImpl.

Spring uses the java.beans.PropertyEditorManager to set the search path for property

editors that might be needed. The search path also includes sun.bean.editors, which includes

PropertyEditor implementations for types such as Font, Color, and most of the primitive types.

Note also that the standard JavaBeans infrastructure will automatically discover PropertyEditor

classes (without you having to register them explicitly) if they are in the same package as the class

they handle, and have the same name as that class, with 'Editor' appended; for example, one could

have the following class and package structure, which would be sufficient for the FooEditor class to

be recognized and used as the PropertyEditor for Foo-typed properties.

com

chank

pop

Foo

FooEditor // the PropertyEditor for the Foo class

Note that you can also use the standard BeanInfo JavaBeans mechanism here as well (described

in not-amazing-detail here). Find below an example of using the BeanInfo mechanism for explicitly

registering one or more PropertyEditor instances with the properties of an associated class.

com

chank

pop

Foo

FooBeanInfo // the BeanInfo for the Foo class

Here is the Java source code for the referenced FooBeanInfo class. This would associate a

CustomNumberEditor with the age property of the Foo class.

public class FooBeanInfo extends SimpleBeanInfo {

public PropertyDescriptor[] getPropertyDescriptors() {

try {

final PropertyEditor numberPE = new CustomNumberEditor(Integer.class, true);

PropertyDescriptor ageDescriptor = new PropertyDescriptor("age", Foo.class) {

public PropertyEditor createPropertyEditor(Object bean) {

return numberPE;

};

return new PropertyDescriptor[] { ageDescriptor };

}

catch (IntrospectionException ex) {

throw new Error(ex.toString());

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 153

Registering additional custom PropertyEditors

When setting bean properties as a string value, a Spring IoC container ultimately uses standard

JavaBeans PropertyEditors to convert these Strings to the complex type of the property. Spring pre-

registers a number of custom PropertyEditors (for example, to convert a classname expressed as

a string into a real Class object). Additionally, Java’s standard JavaBeans PropertyEditor lookup

mechanism allows a PropertyEditor for a class simply to be named appropriately and placed in the

same package as the class it provides support for, to be found automatically.

If there is a need to register other custom PropertyEditors, there are several mechanisms available.

The most manual approach, which is not normally convenient or recommended, is to simply use the

registerCustomEditor() method of the ConfigurableBeanFactory interface, assuming you

have a BeanFactory reference. Another, slightly more convenient, mechanism is to use a special bean

factory post-processor called CustomEditorConfigurer. Although bean factory post-processors can

be used with BeanFactory implementations, the CustomEditorConfigurer has a nested property

setup, so it is strongly recommended that it is used with the ApplicationContext, where it may be

deployed in similar fashion to any other bean, and automatically detected and applied.

Note that all bean factories and application contexts automatically use a number of built-in property

editors, through their use of something called a BeanWrapper to handle property conversions. The

standard property editors that the BeanWrapper registers are listed in the previous section. Additionally,

ApplicationContexts also override or add an additional number of editors to handle resource

lookups in a manner appropriate to the specific application context type.

Standard JavaBeans PropertyEditor instances are used to convert property values expressed as

strings to the actual complex type of the property. CustomEditorConfigurer, a bean factory post-

processor, may be used to conveniently add support for additional PropertyEditor instances to an

ApplicationContext.

Consider a user class ExoticType, and another class DependsOnExoticType which needs

ExoticType set as a property:

package example;

public class ExoticType {

private String name;

public ExoticType(String name) {

this.name = name;

}

public class DependsOnExoticType {

private ExoticType type;

public void setType(ExoticType type) {

this.type = type;

}

When things are properly set up, we want to be able to assign the type property as a string, which a

PropertyEditor will behind the scenes convert into an actual ExoticType instance:

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 154

The PropertyEditor implementation could look similar to this:

// converts string representation to ExoticType object

package example;

public class ExoticTypeEditor extends PropertyEditorSupport {

public void setAsText(String text) {

setValue(new ExoticType(text.toUpperCase()));

}

Finally, we use CustomEditorConfigurer to register the new PropertyEditor with the

ApplicationContext, which will then be able to use it as needed:

<map>

</map>

</property>

</bean>

Using PropertyEditorRegistrars

Another mechanism for registering property editors with the Spring container is to create and

use a PropertyEditorRegistrar. This interface is particularly useful when you need to

use the same set of property editors in several different situations: write a corresponding

registrar and reuse that in each case. PropertyEditorRegistrars work in conjunction with

an interface called PropertyEditorRegistry, an interface that is implemented by the Spring

BeanWrapper (and DataBinder). PropertyEditorRegistrars are particularly convenient when

used in conjunction with the CustomEditorConfigurer (introduced here), which exposes a

property called setPropertyEditorRegistrars(..): PropertyEditorRegistrars added to

a CustomEditorConfigurer in this fashion can easily be shared with DataBinder and Spring

MVC Controllers. Furthermore, it avoids the need for synchronization on custom editors: a

PropertyEditorRegistrar is expected to create fresh PropertyEditor instances for each bean

creation attempt.

Using a PropertyEditorRegistrar is perhaps best illustrated with an example. First off, you need

to create your own PropertyEditorRegistrar implementation:

package com.foo.editors.spring;

public final class CustomPropertyEditorRegistrar implements PropertyEditorRegistrar {

public void registerCustomEditors(PropertyEditorRegistry registry) {

// it is expected that new PropertyEditor instances are created

registry.registerCustomEditor(ExoticType.class, new ExoticTypeEditor());

// you could register as many custom property editors as are required here...

}

See also the org.springframework.beans.support.ResourceEditorRegistrar for an

example PropertyEditorRegistrar implementation. Notice how in its implementation of the

registerCustomEditors(..) method it creates new instances of each property editor.

Next we configure a CustomEditorConfigurer and inject an instance of our

CustomPropertyEditorRegistrar into it:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 155

<list>

</list>

</property>

</bean>

<bean id="customPropertyEditorRegistrar"

class="com.foo.editors.spring.CustomPropertyEditorRegistrar"/>

Finally, and in a bit of a departure from the focus of this chapter, for those of you using Spring’s MVC

web framework, using PropertyEditorRegistrars in conjunction with data-binding Controllers

(such as SimpleFormController) can be very convenient. Find below an example of using a

PropertyEditorRegistrar in the implementation of an initBinder(..) method:

public final class RegisterUserController extends SimpleFormController {

private final PropertyEditorRegistrar customPropertyEditorRegistrar;

public RegisterUserController(PropertyEditorRegistrar propertyEditorRegistrar) {

this.customPropertyEditorRegistrar = propertyEditorRegistrar;

}

protected void initBinder(HttpServletRequest request,

ServletRequestDataBinder binder) throws Exception {

this.customPropertyEditorRegistrar.registerCustomEditors(binder);

}

// other methods to do with registering a User

}

This style of PropertyEditor registration can lead to concise code (the implementation of

initBinder(..) is just one line long!), and allows common PropertyEditor registration code to

be encapsulated in a class and then shared amongst as many Controllers as needed.

7.5 Spring Type Conversion

Spring 3 introduces a core.convert package that provides a general type conversion system. The

system defines an SPI to implement type conversion logic, as well as an API to execute type conversions

at runtime. Within a Spring container, this system can be used as an alternative to PropertyEditors to

convert externalized bean property value strings to required property types. The public API may also be

used anywhere in your application where type conversion is needed.

Converter SPI

The SPI to implement type conversion logic is simple and strongly typed:

package org.springframework.core.convert.converter;

public interface Converter<S, T> {

T convert(S source);

}

To create your own converter, simply implement the interface above. Parameterize S as the type

you are converting from, and T as the type you are converting to. Such a converter can also be

applied transparently if a collection or array of S needs to be converted to an array or collection

of T, provided that a delegating array/collection converter has been registered as well (which

DefaultConversionService does by default).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 156

For each call to convert(S), the source argument is guaranteed to be NOT null. Your Converter

may throw any unchecked exception if conversion fails; specifically, an IllegalArgumentException

should be thrown to report an invalid source value. Take care to ensure that your Converter

implementation is thread-safe.

Several converter implementations are provided in the core.convert.support package as a

convenience. These include converters from Strings to Numbers and other common types. Consider

StringToInteger as an example for a typical Converter implementation:

package org.springframework.core.convert.support;

final class StringToInteger implements Converter<String, Integer> {

public Integer convert(String source) {

return Integer.valueOf(source);

}

ConverterFactory

When you need to centralize the conversion logic for an entire class hierarchy, for example, when

converting from String to java.lang.Enum objects, implement ConverterFactory:

package org.springframework.core.convert.converter;

public interface ConverterFactory<S, R> {

<T extends R> Converter<S, T> getConverter(Class<T> targetType);

}

Parameterize S to be the type you are converting from and R to be the base type defining the range of

classes you can convert to. Then implement getConverter(Class<T>), where T is a subclass of R.

Consider the StringToEnum ConverterFactory as an example:

package org.springframework.core.convert.support;

final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {

public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {

return new StringToEnumConverter(targetType);

}

private final class StringToEnumConverter<T extends Enum> implements Converter<String, T> {

private Class<T> enumType;

public StringToEnumConverter(Class<T> enumType) {

this.enumType = enumType;

}

public T convert(String source) {

return (T) Enum.valueOf(this.enumType, source.trim());

}

GenericConverter

When you require a sophisticated Converter implementation, consider the GenericConverter interface.

With a more flexible but less strongly typed signature, a GenericConverter supports converting between

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 157

multiple source and target types. In addition, a GenericConverter makes available source and target field

context you can use when implementing your conversion logic. Such context allows a type conversion

to be driven by a field annotation, or generic information declared on a field signature.

package org.springframework.core.convert.converter;

public interface GenericConverter {

public Set<ConvertiblePair> getConvertibleTypes();

Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);

}

To implement a GenericConverter, have getConvertibleTypes() return the supported source#target type

pairs. Then implement convert(Object, TypeDescriptor, TypeDescriptor) to implement your conversion

logic. The source TypeDescriptor provides access to the source field holding the value being converted.

The target TypeDescriptor provides access to the target field where the converted value will be set.

A good example of a GenericConverter is a converter that converts between a Java Array and a

Collection. Such an ArrayToCollectionConverter introspects the field that declares the target Collection

type to resolve the Collection’s element type. This allows each element in the source array to be

converted to the Collection element type before the Collection is set on the target field.

Note

Because GenericConverter is a more complex SPI interface, only use it when you need it. Favor

Converter or ConverterFactory for basic type conversion needs.

ConditionalGenericConverter

Sometimes you only want a Converter to execute if a specific condition holds true. For example, you

might only want to execute a Converter if a specific annotation is present on the target field. Or you

might only want to execute a Converter if a specific method, such as static valueOf method, is defined

on the target class. ConditionalGenericConverter is an subinterface of GenericConverter that allows you

to define such custom matching criteria:

public interface ConditionalGenericConverter extends GenericConverter {

boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType);

}

A good example of a ConditionalGenericConverter is an EntityConverter that converts between an

persistent entity identifier and an entity reference. Such a EntityConverter might only match if the target

entity type declares a static finder method e.g. findAccount(Long). You would perform such a finder

method check in the implementation of matches(TypeDescriptor, TypeDescriptor).

ConversionService API

The ConversionService defines a unified API for executing type conversion logic at runtime. Converters

are often executed behind this facade interface:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 158

package org.springframework.core.convert;

public interface ConversionService {

boolean canConvert(Class<?> sourceType, Class<?> targetType);

<T> T convert(Object source, Class<T> targetType);

boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType);

Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);

}

Most ConversionService implementations also implement ConverterRegistry, which provides an

SPI for registering converters. Internally, a ConversionService implementation delegates to its registered

converters to carry out type conversion logic.

A robust ConversionService implementation is provided in the core.convert.support package.

GenericConversionService is the general-purpose implementation suitable for use in most

environments. ConversionServiceFactory provides a convenient factory for creating common

ConversionService configurations.

Configuring a ConversionService

A ConversionService is a stateless object designed to be instantiated at application startup, then shared

between multiple threads. In a Spring application, you typically configure a ConversionService instance

per Spring container (or ApplicationContext). That ConversionService will be picked up by Spring and

then used whenever a type conversion needs to be performed by the framework. You may also inject

this ConversionService into any of your beans and invoke it directly.

Note

If no ConversionService is registered with Spring, the original PropertyEditor-based system is

used.

To register a default ConversionService with Spring, add the following bean definition with id

conversionService:

<bean id="conversionService"

class="org.springframework.context.support.ConversionServiceFactoryBean"/>

A default ConversionService can convert between strings, numbers, enums, collections, maps, and

other common types. To supplement or override the default converters with your own custom

converter(s), set the converters property. Property values may implement either of the Converter,

ConverterFactory, or GenericConverter interfaces.

<bean id="conversionService"

class="org.springframework.context.support.ConversionServiceFactoryBean">

<set>

</set>

</property>

</bean>

It is also common to use a ConversionService within a Spring MVC application. See the section called

“Configuring Formatting in Spring MVC” for details on use with <mvc:annotation-driven/>.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 159

In certain situations you may wish to apply formatting during conversion. See the section called

“FormatterRegistry SPI” for details on using FormattingConversionServiceFactoryBean.

Using a ConversionService programmatically

To work with a ConversionService instance programmatically, simply inject a reference to it like you

would for any other bean:

@Service

public class MyService {

@Autowired

public MyService(ConversionService conversionService) {

this.conversionService = conversionService;

}

public void doIt() {

this.conversionService.convert(...)

}

For most use cases, the convert method specifying the targetType can be used but it will not work with

more complex types such as a collection of a parameterized element. If you want to convert a List of

Integer to a List of String programmatically, for instance, you need to provide a formal definition

of the source and target types.

Fortunately, TypeDescriptor provides various options to make that straightforward:

DefaultConversionService cs = new DefaultConversionService();

List<Integer> input = ....

cs.convert(input,

TypeDescriptor.forObject(input), // List<Integer> type descriptor

TypeDescriptor.collection(List.class, TypeDescriptor.valueOf(String.class)));

Note that DefaultConversionService registers converters automatically which are appropriate for

most environments. This includes collection converters, scalar converters, and also basic Object to

String converters. The same converters can be registered with any ConverterRegistry using the

static addDefaultConverters method on the DefaultConversionService class.

Converters for value types will be reused for arrays and collections, so there is no need to create a

specific converter to convert from a Collection of S to a Collection of T, assuming that standard

collection handling is appropriate.

7.6 Spring Field Formatting

As discussed in the previous section, core.convert is a general-purpose type conversion system. It

provides a unified ConversionService API as well as a strongly-typed Converter SPI for implementing

conversion logic from one type to another. A Spring Container uses this system to bind bean property

values. In addition, both the Spring Expression Language (SpEL) and DataBinder use this system

to bind field values. For example, when SpEL needs to coerce a Short to a Long to complete

an expression.setValue(Object bean, Object value) attempt, the core.convert system

performs the coercion.

Now consider the type conversion requirements of a typical client environment such as a web or desktop

application. In such environments, you typically convert from String to support the client postback

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 160

process, as well as back to String to support the view rendering process. In addition, you often need to

localize String values. The more general core.convert Converter SPI does not address such formatting

requirements directly. To directly address them, Spring 3 introduces a convenient Formatter SPI that

provides a simple and robust alternative to PropertyEditors for client environments.

In general, use the Converter SPI when you need to implement general-purpose type conversion logic;

for example, for converting between a java.util.Date and and java.lang.Long. Use the Formatter SPI

when you’re working in a client environment, such as a web application, and need to parse and print

localized field values. The ConversionService provides a unified type conversion API for both SPIs.

Formatter SPI

The Formatter SPI to implement field formatting logic is simple and strongly typed:

package org.springframework.format;

public interface Formatter<T> extends Printer<T>, Parser<T> {

}

Where Formatter extends from the Printer and Parser building-block interfaces:

public interface Printer<T> {

String print(T fieldValue, Locale locale);

}

import java.text.ParseException;

public interface Parser<T> {

T parse(String clientValue, Locale locale) throws ParseException;

}

To create your own Formatter, simply implement the Formatter interface above. Parameterize T to be the

type of object you wish to format, for example, java.util.Date. Implement the print() operation

to print an instance of T for display in the client locale. Implement the parse() operation to parse an

instance of T from the formatted representation returned from the client locale. Your Formatter should

throw a ParseException or IllegalArgumentException if a parse attempt fails. Take care to ensure your

Formatter implementation is thread-safe.

Several Formatter implementations are provided in format subpackages as a convenience. The

number package provides a NumberFormatter, CurrencyFormatter, and PercentFormatter

to format java.lang.Number objects using a java.text.NumberFormat. The datetime package

provides a DateFormatter to format java.util.Date objects with a java.text.DateFormat.

The datetime.joda package provides comprehensive datetime formatting support based on the Joda

Time library.

Consider DateFormatter as an example Formatter implementation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 161

package org.springframework.format.datetime;

public final class DateFormatter implements Formatter<Date> {

private String pattern;

public DateFormatter(String pattern) {

this.pattern = pattern;

}

public String print(Date date, Locale locale) {

if (date == null) {

return "";

}

return getDateFormat(locale).format(date);

}

public Date parse(String formatted, Locale locale) throws ParseException {

if (formatted.length() == 0) {

return null;

}

return getDateFormat(locale).parse(formatted);

}

protected DateFormat getDateFormat(Locale locale) {

DateFormat dateFormat = new SimpleDateFormat(this.pattern, locale);

dateFormat.setLenient(false);

return dateFormat;

}

The Spring team welcomes community-driven Formatter contributions; see jira.spring.io to contribute.

Annotation-driven Formatting

As you will see, field formatting can be configured by field type or annotation. To bind an Annotation to

a formatter, implement AnnotationFormatterFactory:

package org.springframework.format;

public interface AnnotationFormatterFactory<A extends Annotation> {

Set<Class<?>> getFieldTypes();

Printer<?> getPrinter(A annotation, Class<?> fieldType);

Parser<?> getParser(A annotation, Class<?> fieldType);

}

Parameterize A to be the field annotationType you wish to associate formatting logic

with, for example org.springframework.format.annotation.DateTimeFormat. Have

getFieldTypes() return the types of fields the annotation may be used on. Have getPrinter()

return a Printer to print the value of an annotated field. Have getParser() return a Parser to parse

a clientValue for an annotated field.

The example AnnotationFormatterFactory implementation below binds the @NumberFormat Annotation

to a formatter. This annotation allows either a number style or pattern to be specified:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 162

public final class NumberFormatAnnotationFormatterFactory

implements AnnotationFormatterFactory<NumberFormat> {

public Set<Class<?>> getFieldTypes() {

return new HashSet<Class<?>>(asList(new Class<?>[] {

Short.class, Integer.class, Long.class, Float.class,

Double.class, BigDecimal.class, BigInteger.class }));

}

public Printer<Number> getPrinter(NumberFormat annotation, Class<?> fieldType) {

return configureFormatterFrom(annotation, fieldType);

}

public Parser<Number> getParser(NumberFormat annotation, Class<?> fieldType) {

return configureFormatterFrom(annotation, fieldType);

}

private Formatter<Number> configureFormatterFrom(NumberFormat annotation,

Class<?> fieldType) {

if (!annotation.pattern().isEmpty()) {

return new NumberFormatter(annotation.pattern());

} else {

Style style = annotation.style();

if (style == Style.PERCENT) {

return new PercentFormatter();

} else if (style == Style.CURRENCY) {

return new CurrencyFormatter();

} else {

return new NumberFormatter();

}

To trigger formatting, simply annotate fields with @NumberFormat:

public class MyModel {

@NumberFormat(style=Style.CURRENCY)

private BigDecimal decimal;

}

Format Annotation API

A portable format annotation API exists in the org.springframework.format.annotation

package. Use @NumberFormat to format java.lang.Number fields. Use @DateTimeFormat to format

java.util.Date, java.util.Calendar, java.util.Long, or Joda Time fields.

The example below uses @DateTimeFormat to format a java.util.Date as a ISO Date (yyyy-MM-dd):

public class MyModel {

@DateTimeFormat(iso=ISO.DATE)

private Date date;

}

FormatterRegistry SPI

The FormatterRegistry is an SPI for registering formatters and converters.

FormattingConversionService is an implementation of FormatterRegistry suitable for most

environments. This implementation may be configured programmatically or declaratively as a Spring

bean using FormattingConversionServiceFactoryBean. Because this implementation also

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 163

implements ConversionService, it can be directly configured for use with Spring’s DataBinder and

the Spring Expression Language (SpEL).

Review the FormatterRegistry SPI below:

package org.springframework.format;

public interface FormatterRegistry extends ConverterRegistry {

void addFormatterForFieldType(Class<?> fieldType, Printer<?> printer, Parser<?> parser);

void addFormatterForFieldType(Class<?> fieldType, Formatter<?> formatter);

void addFormatterForFieldType(Formatter<?> formatter);

void addFormatterForAnnotation(AnnotationFormatterFactory<?, ?> factory);

}

As shown above, Formatters can be registered by fieldType or annotation.

The FormatterRegistry SPI allows you to configure Formatting rules centrally, instead of duplicating such

configuration across your Controllers. For example, you might want to enforce that all Date fields are

formatted a certain way, or fields with a specific annotation are formatted in a certain way. With a shared

FormatterRegistry, you define these rules once and they are applied whenever formatting is needed.

FormatterRegistrar SPI

The FormatterRegistrar is an SPI for registering formatters and converters through the

FormatterRegistry:

package org.springframework.format;

public interface FormatterRegistrar {

void registerFormatters(FormatterRegistry registry);

}

A FormatterRegistrar is useful when registering multiple related converters and formatters for a given

formatting category, such as Date formatting. It can also be useful where declarative registration is

insufficient. For example when a formatter needs to be indexed under a specific field type different from

its own <T> or when registering a Printer/Parser pair. The next section provides more information on

converter and formatter registration.

Configuring Formatting in Spring MVC

In a Spring MVC application, you may configure a custom ConversionService instance explicitly as an

attribute of the annotation-driven element of the MVC namespace. This ConversionService will

then be used anytime a type conversion is required during Controller model binding. If not configured

explicitly, Spring MVC will automatically register default formatters and converters for common types

such as numbers and dates.

To rely on default formatting rules, no custom configuration is required in your Spring MVC config XML:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 164

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven/>

</beans>

With this one-line of configuration, default formatters for Numbers and Date types will be installed,

including support for the @NumberFormat and @DateTimeFormat annotations. Full support for the

Joda Time formatting library is also installed if Joda Time is present on the classpath.

To inject a ConversionService instance with custom formatters and converters registered, set the

conversion-service attribute and then specify custom converters, formatters, or FormatterRegistrars as

properties of the FormattingConversionServiceFactoryBean:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven conversion-service="conversionService"/>

<bean id="conversionService"

class="org.springframework.format.support.FormattingConversionServiceFactoryBean">

<set>

</set>

</property>

<set>

</set>

</property>

<set>

</set>

</property>

</bean>

</beans>

Note

See the section called “FormatterRegistrar SPI” and the

FormattingConversionServiceFactoryBean for more information on when to use

FormatterRegistrars.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 165

7.7 Configuring a global date & time format

By default, date and time fields that are not annotated with @DateTimeFormat are converted from

strings using the the DateFormat.SHORT style. If you prefer, you can change this by defining your

own global format.

You will need to ensure that Spring does not register default

formatters, and instead you should register all formatters manually. Use

the org.springframework.format.datetime.joda.JodaTimeFormatterRegistrar or

org.springframework.format.datetime.DateFormatterRegistrar class depending on

whether you use the Joda Time library.

For example, the following Java configuration will register a global ' yyyyMMdd' format. This example

does not depend on the Joda Time library:

@Configuration

public class AppConfig {

@Bean

public FormattingConversionService conversionService() {

// Use the DefaultFormattingConversionService but do not register defaults

DefaultFormattingConversionService conversionService = new

DefaultFormattingConversionService(false);

// Ensure @NumberFormat is still supported

conversionService.addFormatterForFieldAnnotation(new NumberFormatAnnotationFormatterFactory());

// Register date conversion with a specific global format

DateFormatterRegistrar registrar = new DateFormatterRegistrar();

registrar.setFormatter(new DateFormatter("yyyyMMdd"));

registrar.registerFormatters(conversionService);

return conversionService;

}

If you prefer XML based configuration you can use a

FormattingConversionServiceFactoryBean. Here is the same example, this time using Joda

Time:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 166

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd>

<bean

id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean">

<set>

<bean class="org.springframework.format.number.NumberFormatAnnotationFormatterFactory" /

</set>

</property>

<set>

</bean>

</property>

</bean>

</set>

</property>

</bean>

</beans>

Note

Joda Time provides separate distinct types to represent date, time and date-time

values. The dateFormatter, timeFormatter and dateTimeFormatter properties of the

JodaTimeFormatterRegistrar should be used to configure the different formats for each

type. The DateTimeFormatterFactoryBean provides a convenient way to create formatters.

If you are using Spring MVC remember to explicitly configure the conversion service that is used. For

Java based @Configuration this means extending the WebMvcConfigurationSupport class and

overriding the mvcConversionService() method. For XML you should use the 'conversion-

service' attribute of the mvc:annotation-driven element. See the section called “Configuring

Formatting in Spring MVC” for details.

7.8 Spring Validation

Spring 3 introduces several enhancements to its validation support. First, the JSR-303 Bean Validation

API is now fully supported. Second, when used programmatically, Spring’s DataBinder can now validate

objects as well as bind to them. Third, Spring MVC now has support for declaratively validating

@Controller inputs.

Overview of the JSR-303 Bean Validation API

JSR-303 standardizes validation constraint declaration and metadata for the Java platform. Using this

API, you annotate domain model properties with declarative validation constraints and the runtime

enforces them. There are a number of built-in constraints you can take advantage of. You may also

define your own custom constraints.

To illustrate, consider a simple PersonForm model with two properties:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 167

public class PersonForm {

private String name;

private int age;

}

JSR-303 allows you to define declarative validation constraints against such properties:

public class PersonForm {

@NotNull

@Size(max=64)

private String name;

@Min(0)

private int age;

}

When an instance of this class is validated by a JSR-303 Validator, these constraints will be enforced.

For general information on JSR-303/JSR-349, see the Bean Validation website. For information on the

specific capabilities of the default reference implementation, see the Hibernate Validator documentation.

To learn how to setup a Bean Validation provider as a Spring bean, keep reading.

Configuring a Bean Validation Provider

Spring provides full support for the Bean Validation API. This includes convenient support for

bootstrapping a JSR-303/JSR-349 Bean Validation provider as a Spring bean. This allows for

a javax.validation.ValidatorFactory or javax.validation.Validator to be injected

wherever validation is needed in your application.

Use the LocalValidatorFactoryBean to configure a default Validator as a Spring bean:

<bean id="validator"

class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>

The basic configuration above will trigger Bean Validation to initialize using its default bootstrap

mechanism. A JSR-303/JSR-349 provider, such as Hibernate Validator, is expected to be present in

the classpath and will be detected automatically.

Injecting a Validator

LocalValidatorFactoryBean implements both javax.validation.ValidatorFactory and

javax.validation.Validator, as well as Spring’s

org.springframework.validation.Validator. You may inject a reference to either of these

interfaces into beans that need to invoke validation logic.

Inject a reference to javax.validation.Validator if you prefer to work with the Bean Validation

API directly:

import javax.validation.Validator;

@Service

public class MyService {

@Autowired

private Validator validator;

Inject a reference to org.springframework.validation.Validator if your bean requires the

Spring Validation API:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 168

import org.springframework.validation.Validator;

@Service

public class MyService {

@Autowired

private Validator validator;

}

Configuring Custom Constraints

Each Bean Validation constraint consists of two parts. First, a @Constraint annotation

that declares the constraint and its configurable properties. Second, an implementation of

the javax.validation.ConstraintValidator interface that implements the constraint’s

behavior. To associate a declaration with an implementation, each @Constraint annotation

references a corresponding ValidationConstraint implementation class. At runtime, a

ConstraintValidatorFactory instantiates the referenced implementation when the constraint

annotation is encountered in your domain model.

By default, the LocalValidatorFactoryBean configures a

SpringConstraintValidatorFactory that uses Spring to create ConstraintValidator instances.

This allows your custom ConstraintValidators to benefit from dependency injection like any other Spring

bean.

Shown below is an example of a custom @Constraint declaration, followed by an associated

ConstraintValidator implementation that uses Spring for dependency injection:

@Target({ElementType.METHOD, ElementType.FIELD})

@Retention(RetentionPolicy.RUNTIME)

@Constraint(validatedBy=MyConstraintValidator.class)

public @interface MyConstraint {

}

import javax.validation.ConstraintValidator;

public class MyConstraintValidator implements ConstraintValidator {

@Autowired;

private Foo aDependency;

...

}

As you can see, a ConstraintValidator implementation may have its dependencies @Autowired like any

other Spring bean.

Spring-driven Method Validation

The method validation feature supported by Bean Validation 1.1, and as a custom extension

also by Hibernate Validator 4.3, can be integrated into a Spring context through a

MethodValidationPostProcessor bean definition:

In order to be eligible for Spring-driven method validation, all target classes need to be annotated

with Spring’s @Validated annotation, optionally declaring the validation groups to use. Check out the

MethodValidationPostProcessor javadocs for setup details with Hibernate Validator and Bean

Validation 1.1 providers.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 169

Additional Configuration Options

The default LocalValidatorFactoryBean configuration should prove sufficient for most cases.

There are a number of configuration options for various Bean Validation constructs, from message

interpolation to traversal resolution. See the LocalValidatorFactoryBean javadocs for more

information on these options.

Configuring a DataBinder

Since Spring 3, a DataBinder instance can be configured with a Validator. Once configured, the Validator

may be invoked by calling binder.validate(). Any validation Errors are automatically added to the

binder’s BindingResult.

When working with the DataBinder programmatically, this can be used to invoke validation logic after

binding to a target object:

Foo target = new Foo();

DataBinder binder = new DataBinder(target);

binder.setValidator(new FooValidator());

// bind to the target object

binder.bind(propertyValues);

// validate the target object

binder.validate();

// get BindingResult that includes any validation errors

BindingResult results = binder.getBindingResult();

A DataBinder can also be configured with multiple Validator instances via

dataBinder.addValidators and dataBinder.replaceValidators. This is useful when

combining globally configured Bean Validation with a Spring Validator configured locally on a

DataBinder instance. See the section called “Configuring a Validator for use by Spring MVC”.

Spring MVC 3 Validation

Beginning with Spring 3, Spring MVC has the ability to automatically validate @Controller inputs. In

previous versions it was up to the developer to manually invoke validation logic.

Triggering @Controller Input Validation

To trigger validation of a @Controller input, simply annotate the input argument as @Valid:

@Controller

public class MyController {

@RequestMapping("/foo", method=RequestMethod.POST)

public void processFoo(@Valid Foo foo) { /* ... */ }

Spring MVC will validate a @Valid object after binding so-long as an appropriate Validator has been

configured.

Note

The @Valid annotation is part of the standard JSR-303 Bean Validation API, and is not a Spring-

specific construct.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 170

Configuring a Validator for use by Spring MVC

The Validator instance invoked when a @Valid method argument is encountered may be configured

in two ways. First, you may call binder.setValidator(Validator) within a @Controller's

@InitBinder callback. This allows you to configure a Validator instance per @Controller class:

@Controller

public class MyController {

@InitBinder

protected void initBinder(WebDataBinder binder) {

binder.setValidator(new FooValidator());

}

@RequestMapping("/foo", method=RequestMethod.POST)

public void processFoo(@Valid Foo foo) { ... }

}

Second, you may call setValidator(Validator) on the global WebBindingInitializer. This

allows you to configure a Validator instance across all @Controller classes. This can be achieved

easily by using the Spring MVC namespace:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven validator="globalValidator"/>

</beans>

To combine a global and a local validator, configure the global validator as shown above and then add

a local validator:

@Controller

public class MyController {

@InitBinder

protected void initBinder(WebDataBinder binder) {

binder.addValidators(new FooValidator());

}

Configuring a JSR-303/JSR-349 Validator for use by Spring MVC

With Bean Validation, a single javax.validation.Validator instance typically validates all model

objects that declare validation constraints. To configure such a JSR-303 backed Validator with Spring

MVC, simply add a Bean Validation provider, such as Hibernate Validator, to your classpath. Spring

MVC will detect it and automatically enable Bean Validation support across all Controllers.

The Spring MVC configuration required to enable Bean Validation support is shown below:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 171

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven/>

</beans>

With this minimal configuration, anytime a @Valid @Controller input is encountered, it will be

validated by the Bean Validation provider. That provider, in turn, will enforce any constraints declared

against the input. Any ConstraintViolations will automatically be exposed as errors in the

BindingResult renderable by standard Spring MVC form tags.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 172

8. Spring Expression Language (SpEL)

8.1 Introduction

The Spring Expression Language (SpEL for short) is a powerful expression language that supports

querying and manipulating an object graph at runtime. The language syntax is similar to Unified EL but

offers additional features, most notably method invocation and basic string templating functionality.

While there are several other Java expression languages available, OGNL, MVEL, and JBoss EL, to

name a few, the Spring Expression Language was created to provide the Spring community with a single

well supported expression language that can be used across all the products in the Spring portfolio.

Its language features are driven by the requirements of the projects in the Spring portfolio, including

tooling requirements for code completion support within the eclipse based Spring Tool Suite. That said,

SpEL is based on a technology agnostic API allowing other expression language implementations to

be integrated should the need arise.

While SpEL serves as the foundation for expression evaluation within the Spring portfolio, it is not directly

tied to Spring and can be used independently. In order to be self contained, many of the examples in

this chapter use SpEL as if it were an independent expression language. This requires creating a few

bootstrapping infrastructure classes such as the parser. Most Spring users will not need to deal with this

infrastructure and will instead only author expression strings for evaluation. An example of this typical

use is the integration of SpEL into creating XML or annotated based bean definitions as shown in the

section Expression support for defining bean definitions.

This chapter covers the features of the expression language, its API, and its language syntax. In several

places an Inventor and Inventor’s Society class are used as the target objects for expression evaluation.

These class declarations and the data used to populate them are listed at the end of the chapter.

8.2 Feature Overview

The expression language supports the following functionality

• Literal expressions

• Boolean and relational operators

• Regular expressions

• Class expressions

• Accessing properties, arrays, lists, maps

• Method invocation

• Relational operators

• Assignment

• Calling constructors

• Bean references

• Array construction

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 173

• Inline lists

• Inline maps

• Ternary operator

• Variables

• User defined functions

• Collection projection

• Collection selection

• Templated expressions

8.3 Expression Evaluation using Spring’s Expression Interface

This section introduces the simple use of SpEL interfaces and its expression language. The complete

language reference can be found in the section Language Reference.

The following code introduces the SpEL API to evaluate the literal string expression Hello World.

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("'Hello World'");

String message = (String) exp.getValue();

The value of the message variable is simply Hello World.

The SpEL classes and interfaces you are most likely to use are located in the packages

org.springframework.expression and its sub packages and spel.support.

The interface ExpressionParser is responsible for parsing an expression string. In this example

the expression string is a string literal denoted by the surrounding single quotes. The interface

Expression is responsible for evaluating the previously defined expression string. There are two

exceptions that can be thrown, ParseException and EvaluationException when calling '

parser.parseExpression' and ' exp.getValue' respectively.

SpEL supports a wide range of features, such as calling methods, accessing properties, and calling

constructors.

As an example of method invocation, we call the concat method on the string literal.

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("'Hello World'.concat('!')");

String message = (String) exp.getValue();

The value of message is now Hello World!.

As an example of calling a JavaBean property, the String property Bytes can be called as shown below.

ExpressionParser parser = new SpelExpressionParser();

// invokes getBytes()

Expression exp = parser.parseExpression("'Hello World'.bytes");

byte[] bytes = (byte[]) exp.getValue();

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 174

SpEL also supports nested properties using standard dot notation, i.e. prop1.prop2.prop3 and the setting

of property values

Public fields may also be accessed.

ExpressionParser parser = new SpelExpressionParser();

// invokes getBytes().length

Expression exp = parser.parseExpression("'Hello World'.bytes.length");

int length = (Integer) exp.getValue();

The String’s constructor can be called instead of using a string literal.

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("new String('hello world').toUpperCase()");

String message = exp.getValue(String.class);

Note the use of the generic method public <T> T getValue(Class<T> desiredResultType).

Using this method removes the need to cast the value of the expression to the desired result type. An

EvaluationException will be thrown if the value cannot be cast to the type T or converted using

the registered type converter.

The more common usage of SpEL is to provide an expression string that is evaluated against a specific

object instance (called the root object). There are two options here and which to choose depends on

whether the object against which the expression is being evaluated will be changing with each call to

evaluate the expression. In the following example we retrieve the name property from an instance of

the Inventor class.

// Create and set a calendar

GregorianCalendar c = new GregorianCalendar();

c.set(1856, 7, 9);

// The constructor arguments are name, birthday, and nationality.

Inventor tesla = new Inventor("Nikola Tesla", c.getTime(), "Serbian");

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("name");

EvaluationContext context = new StandardEvaluationContext(tesla);

String name = (String) exp.getValue(context);

In the last line, the value of the string variable name will be set to "Nikola Tesla". The class

StandardEvaluationContext is where you can specify which object the "name" property will be evaluated

against. This is the mechanism to use if the root object is unlikely to change, it can simply be set once

in the evaluation context. If the root object is likely to change repeatedly, it can be supplied on each call

to getValue, as this next example shows:

/ Create and set a calendar

GregorianCalendar c = new GregorianCalendar();

c.set(1856, 7, 9);

// The constructor arguments are name, birthday, and nationality.

Inventor tesla = new Inventor("Nikola Tesla", c.getTime(), "Serbian");

ExpressionParser parser = new SpelExpressionParser();

Expression exp = parser.parseExpression("name");

String name = (String) exp.getValue(tesla);

In this case the inventor tesla has been supplied directly to getValue and the expression evaluation

infrastructure creates and manages a default evaluation context internally - it did not require one to be

supplied.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 175

The StandardEvaluationContext is relatively expensive to construct and during repeated usage it builds

up cached state that enables subsequent expression evaluations to be performed more quickly. For

this reason it is better to cache and reuse them where possible, rather than construct a new one for

each expression evaluation.

In some cases it can be desirable to use a configured evaluation context and yet still supply a different

root object on each call to getValue. getValue allows both to be specified on the same call. In these

situations the root object passed on the call is considered to override any (which maybe null) specified

on the evaluation context.

Note

In standalone usage of SpEL there is a need to create the parser, parse expressions and perhaps

provide evaluation contexts and a root context object. However, more common usage is to provide

only the SpEL expression string as part of a configuration file, for example for Spring bean or

Spring Web Flow definitions. In this case, the parser, evaluation context, root object and any

predefined variables are all set up implicitly, requiring the user to specify nothing other than the

expressions.

As a final introductory example, the use of a boolean operator is shown using the Inventor object in

the previous example.

Expression exp = parser.parseExpression("name == Nikola Tesla");

boolean result = exp.getValue(context, Boolean.class); // evaluates to true

The EvaluationContext interface

The interface EvaluationContext is used when evaluating an expression to resolve

properties, methods, fields, and to help perform type conversion. The out-of-the-box

implementation, StandardEvaluationContext, uses reflection to manipulate the object, caching

java.lang.reflect's Method, Field, and Constructor instances for increased performance.

The StandardEvaluationContext is where you may specify the root object to evaluate against via

the method setRootObject() or passing the root object into the constructor. You can also specify

variables and functions that will be used in the expression using the methods setVariable() and

registerFunction(). The use of variables and functions are described in the language reference

sections Variables and Functions. The StandardEvaluationContext is also where you can register

custom ConstructorResolvers, MethodResolvers, and PropertyAccessors to extend how

SpEL evaluates expressions. Please refer to the JavaDoc of these classes for more details.

Type Conversion

By default SpEL uses the conversion service available in Spring core (

org.springframework.core.convert.ConversionService). This conversion service comes

with many converters built in for common conversions but is also fully extensible so custom conversions

between types can be added. Additionally it has the key capability that it is generics aware. This means

that when working with generic types in expressions, SpEL will attempt conversions to maintain type

correctness for any objects it encounters.

What does this mean in practice? Suppose assignment, using setValue(), is being used to set a List

property. The type of the property is actually List<Boolean>. SpEL will recognize that the elements

of the list need to be converted to Boolean before being placed in it. A simple example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 176

class Simple {

public List<Boolean> booleanList = new ArrayList<Boolean>();

}

Simple simple = new Simple();

simple.booleanList.add(true);

StandardEvaluationContext simpleContext = new StandardEvaluationContext(simple);

// false is passed in here as a string. SpEL and the conversion service will

// correctly recognize that it needs to be a Boolean and convert it

parser.parseExpression("booleanList[0]").setValue(simpleContext, "false");

// b will be false

Boolean b = simple.booleanList.get(0);

Parser configuration

It is possible to configure the SpEL expression parser using a parser configuration object

(org.springframework.expression.spel.SpelParserConfiguration). The configuration

object controls the behaviour of some of the expression components. For example, if indexing into an

array or collection and the element at the specified index is null it is possible to automatically create the

element. This is useful when using expressions made up of a chain of property references. If indexing

into an array or list and specifying an index that is beyond the end of the current size of the array or list

it is possible to automatically grow the array or list to accommodate that index.

class Demo {

public List<String> list;

}

// Turn on:

// - auto null reference initialization

// - auto collection growing

SpelParserConfiguration config = new SpelParserConfiguration(true,true);

ExpressionParser parser = new SpelExpressionParser(config);

Expression expression = parser.parseExpression("list[3]");

Demo demo = new Demo();

Object o = expression.getValue(demo);

// demo.list will now be a real collection of 4 entries

// Each entry is a new empty String

It is also possible to configure the behaviour of the SpEL expression compiler.

SpEL compilation

Spring Framework 4.1 includes a basic expression compiler. Expressions are usually interpreted which

provides a lot of dynamic flexibility during evaluation but does not provide the optimum performance. For

occasional expression usage this is fine, but when used by other components like Spring Integration,

performance can be very important and there is no real need for the dynamism.

The new SpEL compiler is intended to address this need. The compiler will generate a real Java

class on the fly during evaluation that embodies the expression behaviour and use that to achieve

much faster expression evaluation. Due to the lack of typing around expressions the compiler uses

information gathered during the interpreted evaluations of an expression when performing compilation.

For example, it does not know the type of a property reference purely from the expression but during the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 177

first interpreted evaluation it will find out what it is. Of course, basing the compilation on this information

could cause trouble later if the types of the various expression elements change over time. For this

reason compilation is best suited to expressions whose type information is not going to change on

repeated evaluations.

For a basic expression like this:

someArray[0].someProperty.someOtherProperty < 0.1

which involves array access, some property derefencing and numeric operations, the performance gain

can be very noticeable. In an example microbenchmark run of 50000 iterations, it was taking 75ms to

evaluate using only the interpreter and just 3ms using the compiled version of the expression.

Compiler configuration

The compiler is not turned on by default, there are two ways to turn it on. It can be turned on using the

parser configuration process discussed earlier or via a system property when SpEL usage is embedded

inside another component. This section discussed both of these options.

Is is important to understand that there are a few modes the compiler can operate in, captured in an enum

(org.springframework.expression.spel.SpelCompilerMode). The modes are as follows:

•OFF - the compiler is switched off, this is the default.

•IMMEDIATE - In immediate mode the expressions are compiled as soon as possible. This is typically

after the first interpreted evaluation. If the compiled expression fails (typically due to a type changing,

as described above) then the caller of the expression evaluation will receive an exception.

•MIXED - In mixed mode the expressions silently switch between interpreted and compiled mode over

time. After some number of interpreted runs they will switch to compiled form and if something goes

wrong with the compiled form (like a type changing, as described above) then the expression will

automatically switch back to interpreted form again. Sometime later it may generate another compiled

form and switch to it. Basically the exception that the user gets in IMMEDIATE mode is instead handled

internally.

IMMEDIATE mode exists because MIXED mode could cause issues for expressions that have side

effects. If a compiled expression blows up after partially succeeding it may have already done something

that has affected the state of the system. If this has happened the caller may not want it to silently re-

run in interpreted mode since part of the expression may be running twice.

After selecting a mode, use the SpelParserConfiguration to configure the parser:

SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE,

this.getClass().getClassLoader());

SpelExpressionParser parser = new SpelExpressionParser(config);

Expression expr = parser.parseExpression("payload");

MyMessage message = new MyMessage();

Object payload = expr.getValue(message);

When specifying the compiler mode it is also possible to specify a classloader (passing null is allowed).

Compiled expressions will be defined in a child classloader created under any that is supplied. It is

important to ensure if a classloader is specified it can see all the types involved in the expression

evaluation process. If none is specified then a default classloader will be used (typically the context

classloader for the thread that is running during expression evaluation).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 178

The second way to configure the compiler is for use when SpEL is embedded inside some other

component and it may not be possible to configure via a configuration object. In these cases it is possible

to use a system property. The property spring.expression.compiler.mode can be set to one of

the SpelCompilerMode enum values (off, immediate or mixed).

Compiler limitations

With Spring Framework 4.1 the basic compilation framework is in place. However, the framework

does not yet support compiling every kind of expression. The initial focus has been on the common

expressions that are likely to be used in performance critical contexts. These kinds of expression cannot

be compiled at the moment:

• expressions involving assignment

• expressions relying on the conversion service

• expressions using custom resolvers or accessors

• expressions using selection or projection

More and more types of expression will be compilable in the future.

8.4 Expression support for defining bean definitions

SpEL expressions can be used with XML or annotation-based configuration metadata for defining

BeanDefinitions. In both cases the syntax to define the expression is of the form #{ <expression

string> }.

XML based configuration

A property or constructor-arg value can be set using expressions as shown below.

</bean>

The variable systemProperties is predefined, so you can use it in your expressions as shown below.

Note that you do not have to prefix the predefined variable with the # symbol in this context.

</bean>

You can also refer to other bean properties by name, for example.

</bean>

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 179

Annotation-based configuration

The @Value annotation can be placed on fields, methods and method/constructor parameters to specify

a default value.

Here is an example to set the default value of a field variable.

public static class FieldValueTestBean

@Value("#{ systemProperties[user.region] }")

private String defaultLocale;

public void setDefaultLocale(String defaultLocale) {

this.defaultLocale = defaultLocale;

}

public String getDefaultLocale() {

return this.defaultLocale;

}

The equivalent but on a property setter method is shown below.

public static class PropertyValueTestBean

private String defaultLocale;

@Value("#{ systemProperties[user.region] }")

public void setDefaultLocale(String defaultLocale) {

this.defaultLocale = defaultLocale;

}

public String getDefaultLocale() {

return this.defaultLocale;

}

Autowired methods and constructors can also use the @Value annotation.

public class SimpleMovieLister {

private MovieFinder movieFinder;

private String defaultLocale;

@Autowired

public void configure(MovieFinder movieFinder,

@Value("#{ systemProperties[user.region] }") String defaultLocale) {

this.movieFinder = movieFinder;

this.defaultLocale = defaultLocale;

}

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 180

public class MovieRecommender {

private String defaultLocale;

private CustomerPreferenceDao customerPreferenceDao;

@Autowired

public MovieRecommender(CustomerPreferenceDao customerPreferenceDao,

@Value("#{systemProperties[user.country]}") String defaultLocale) {

this.customerPreferenceDao = customerPreferenceDao;

this.defaultLocale = defaultLocale;

}

// ...

}

8.5 Language Reference

Literal expressions

The types of literal expressions supported are strings, dates, numeric values (int, real, and hex), boolean

and null. Strings are delimited by single quotes. To put a single quote itself in a string use two single

quote characters. The following listing shows simple usage of literals. Typically they would not be used

in isolation like this, but as part of a more complex expression, for example using a literal on one side

of a logical comparison operator.

ExpressionParser parser = new SpelExpressionParser();

// evals to "Hello World"

String helloWorld = (String) parser.parseExpression("Hello World").getValue();

double avogadrosNumber = (Double) parser.parseExpression("6.0221415E+23").getValue();

// evals to 2147483647

int maxValue = (Integer) parser.parseExpression("0x7FFFFFFF").getValue();

boolean trueValue = (Boolean) parser.parseExpression("true").getValue();

Object nullValue = parser.parseExpression("null").getValue();

Numbers support the use of the negative sign, exponential notation, and decimal points. By default real

numbers are parsed using Double.parseDouble().

Properties, Arrays, Lists, Maps, Indexers

Navigating with property references is easy: just use a period to indicate a nested property value. The

instances of the Inventor class, pupin, and tesla, were populated with data listed in the section Classes

used in the examples. To navigate "down" and get Tesla’s year of birth and Pupin’s city of birth the

following expressions are used.

// evals to 1856

int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);

Case insensitivity is allowed for the first letter of property names. The contents of arrays and lists are

obtained using square bracket notation.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 181

ExpressionParser parser = new SpelExpressionParser();

// Inventions Array

StandardEvaluationContext teslaContext = new StandardEvaluationContext(tesla);

// evaluates to "Induction motor"

String invention = parser.parseExpression("inventions[3]").getValue(

teslaContext, String.class);

// Members List

StandardEvaluationContext societyContext = new StandardEvaluationContext(ieee);

// evaluates to "Nikola Tesla"

String name = parser.parseExpression("Members[0].Name").getValue(

societyContext, String.class);

// List and Array navigation

// evaluates to "Wireless communication"

String invention = parser.parseExpression("Members[0].Inventions[6]").getValue(

societyContext, String.class);

The contents of maps are obtained by specifying the literal key value within the brackets. In this case,

because keys for the Officers map are strings, we can specify string literals.

// Officer's Dictionary

Inventor pupin = parser.parseExpression("Officers[president]").getValue(

societyContext, Inventor.class);

// evaluates to "Idvor"

String city = parser.parseExpression("Officers[president].PlaceOfBirth.City").getValue(

societyContext, String.class);

// setting values

parser.parseExpression("Officers[advisors][0].PlaceOfBirth.Country").setValue(

societyContext, "Croatia");

Inline lists

Lists can be expressed directly in an expression using {} notation.

// evaluates to a Java list containing the four numbers

List numbers = (List) parser.parseExpression("{1,2,3,4}").getValue(context);

List listOfLists = (List) parser.parseExpression("{{a,b},{x,y}}").getValue(context);

{} by itself means an empty list. For performance reasons, if the list is itself entirely composed of fixed

literals then a constant list is created to represent the expression, rather than building a new list on

each evaluation.

Inline Maps

Maps can also be expressed directly in an expression using {key:value} notation.

// evaluates to a Java map containing the two entries

Map inventorInfo = (Map) parser.parseExpression("{name:'Nikola',dob:'10-July-1856'}").getValue(context);

Map mapOfMaps = (Map) parser.parseExpression("{name:{first:'Nikola',last:'Tesla'},dob:

{day:10,month:'July',year:1856}}").getValue(context);

{:} by itself means an empty map. For performance reasons, if the map is itself composed of fixed

literals or other nested constant structures (lists or maps) then a constant map is created to represent

the expression, rather than building a new map on each evaluation. Quoting of the map keys is optional,

the examples above are not using quoted keys.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 182

Array construction

Arrays can be built using the familiar Java syntax, optionally supplying an initializer to have the array

populated at construction time.

int[] numbers1 = (int[]) parser.parseExpression("new int[4]").getValue(context);

// Array with initializer

int[] numbers2 = (int[]) parser.parseExpression("new int[]{1,2,3}").getValue(context);

// Multi dimensional array

int[][] numbers3 = (int[][]) parser.parseExpression("new int[4][5]").getValue(context);

It is not currently allowed to supply an initializer when constructing a multi-dimensional array.

Methods

Methods are invoked using typical Java programming syntax. You may also invoke methods on literals.

Varargs are also supported.

// string literal, evaluates to "bc"

String c = parser.parseExpression("abc.substring(2, 3)").getValue(String.class);

// evaluates to true

boolean isMember = parser.parseExpression("isMember(Mihajlo Pupin)").getValue(

societyContext, Boolean.class);

Operators

Relational operators

The relational operators; equal, not equal, less than, less than or equal, greater than, and greater than

or equal are supported using standard operator notation.

// evaluates to true

boolean trueValue = parser.parseExpression("2 == 2").getValue(Boolean.class);

// evaluates to false

boolean falseValue = parser.parseExpression("2 < -5.0").getValue(Boolean.class);

// evaluates to true

boolean trueValue = parser.parseExpression("black < block").getValue(Boolean.class);

In addition to standard relational operators SpEL supports the instanceof and regular expression

based matches operator.

// evaluates to false

boolean falseValue = parser.parseExpression(

"'xyz' instanceof T(int)").getValue(Boolean.class);

// evaluates to true

boolean trueValue = parser.parseExpression(

"'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);

//evaluates to false

boolean falseValue = parser.parseExpression(

"'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);

Each symbolic operator can also be specified as a purely alphabetic equivalent. This avoids problems

where the symbols used have special meaning for the document type in which the expression is

embedded (eg. an XML document). The textual equivalents are shown here: lt (<), gt (>), le (<=), ge

(>=), eq (==), ne (!=), div (/), mod (%), not (!). These are case insensitive.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 183

Logical operators

The logical operators that are supported are and, or, and not. Their use is demonstrated below.

// -- AND --

// evaluates to false

boolean falseValue = parser.parseExpression("true and false").getValue(Boolean.class);

// evaluates to true

String expression = "isMember(Nikola Tesla) and isMember(Mihajlo Pupin)";

boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

// -- OR --

// evaluates to true

boolean trueValue = parser.parseExpression("true or false").getValue(Boolean.class);

// evaluates to true

String expression = "isMember(Nikola Tesla) or isMember(Albert Einstein)";

boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

// -- NOT --

// evaluates to false

boolean falseValue = parser.parseExpression("!true").getValue(Boolean.class);

// -- AND and NOT --

String expression = "isMember(Nikola Tesla) and !isMember(Mihajlo Pupin)";

boolean falseValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);

Mathematical operators

The addition operator can be used on both numbers and strings. Subtraction, multiplication and

division can be used only on numbers. Other mathematical operators supported are modulus (%) and

exponential power (^). Standard operator precedence is enforced. These operators are demonstrated

below.

// Addition

int two = parser.parseExpression("1 + 1").getValue(Integer.class); // 2

String testString = parser.parseExpression(

"test + ' ' + string").getValue(String.class); // test string

// Subtraction

int four = parser.parseExpression("1 - -3").getValue(Integer.class); // 4

double d = parser.parseExpression("1000.00 - 1e4").getValue(Double.class); // -9000

// Multiplication

int six = parser.parseExpression("-2 * -3").getValue(Integer.class); // 6

double twentyFour = parser.parseExpression("2.0 * 3e0 * 4").getValue(Double.class); // 24.0

// Division

int minusTwo = parser.parseExpression("6 / -3").getValue(Integer.class); // -2

double one = parser.parseExpression("8.0 / 4e0 / 2").getValue(Double.class); // 1.0

// Modulus

int three = parser.parseExpression("7 % 4").getValue(Integer.class); // 3

int one = parser.parseExpression("8 / 5 % 2").getValue(Integer.class); // 1

// Operator precedence

int minusTwentyOne = parser.parseExpression("1+2-3*8").getValue(Integer.class); // -21

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 184

Assignment

Setting of a property is done by using the assignment operator. This would typically be done within a

call to setValue but can also be done inside a call to getValue.

Inventor inventor = new Inventor();

StandardEvaluationContext inventorContext = new StandardEvaluationContext(inventor);

parser.parseExpression("Name").setValue(inventorContext, "Alexander Seovic2");

// alternatively

String aleks = parser.parseExpression(

"Name = Alexandar Seovic").getValue(inventorContext, String.class);

Types

The special T operator can be used to specify an instance of java.lang.Class (the type). Static methods

are invoked using this operator as well. The StandardEvaluationContext uses a TypeLocator

to find types and the StandardTypeLocator (which can be replaced) is built with an understanding

of the java.lang package. This means T() references to types within java.lang do not need to be fully

qualified, but all other type references must be.

Class dateClass = parser.parseExpression("T(java.util.Date)").getValue(Class.class);

Class stringClass = parser.parseExpression("T(String)").getValue(Class.class);

boolean trueValue = parser.parseExpression(

"T(java.math.RoundingMode).CEILING < T(java.math.RoundingMode).FLOOR")

.getValue(Boolean.class);

Constructors

Constructors can be invoked using the new operator. The fully qualified class name should be used for

all but the primitive type and String (where int, float, etc, can be used).

Inventor einstein = p.parseExpression(

"new org.spring.samples.spel.inventor.Inventor(Albert Einstein, German)")

.getValue(Inventor.class);

//create new inventor instance within add method of List

p.parseExpression(

"Members.add(new org.spring.samples.spel.inventor.Inventor(

Albert Einstein, German))").getValue(societyContext);

Variables

Variables can be referenced in the expression using the syntax #variableName. Variables are set

using the method setVariable on the StandardEvaluationContext.

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");

StandardEvaluationContext context = new StandardEvaluationContext(tesla);

context.setVariable("newName", "Mike Tesla");

parser.parseExpression("Name = #newName").getValue(context);

System.out.println(tesla.getName()) // "Mike Tesla"

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 185

The #this and #root variables

The variable #this is always defined and refers to the current evaluation object (against which unqualified

references are resolved). The variable #root is always defined and refers to the root context object.

Although #this may vary as components of an expression are evaluated, #root always refers to the root.

// create an array of integers

List<Integer> primes = new ArrayList<Integer>();

primes.addAll(Arrays.asList(2,3,5,7,11,13,17));

// create parser and set variable primes as the array of integers

ExpressionParser parser = new SpelExpressionParser();

StandardEvaluationContext context = new StandardEvaluationContext();

context.setVariable("primes",primes);

// all prime numbers > 10 from the list (using selection ?{...})

// evaluates to [11, 13, 17]

List<Integer> primesGreaterThanTen = (List<Integer>) parser.parseExpression(

"#primes.?[#this>10]").getValue(context);

Functions

You can extend SpEL by registering user defined functions that can be called within the expression

string. The function is registered with the StandardEvaluationContext using the method.

public void registerFunction(String name, Method m)

A reference to a Java Method provides the implementation of the function. For example, a utility method

to reverse a string is shown below.

public abstract class StringUtils {

public static String reverseString(String input) {

StringBuilder backwards = new StringBuilder();

for (int i = 0; i < input.length(); i++)

backwards.append(input.charAt(input.length() - 1 - i));

}

return backwards.toString();

}

This method is then registered with the evaluation context and can be used within an expression string.

ExpressionParser parser = new SpelExpressionParser();

StandardEvaluationContext context = new StandardEvaluationContext();

context.registerFunction("reverseString",

StringUtils.class.getDeclaredMethod("reverseString", new Class[] { String.class }));

String helloWorldReversed = parser.parseExpression(

"#reverseString(hello)").getValue(context, String.class);

Bean references

If the evaluation context has been configured with a bean resolver it is possible to lookup beans from

an expression using the (@) symbol.

ExpressionParser parser = new SpelExpressionParser();

StandardEvaluationContext context = new StandardEvaluationContext();

context.setBeanResolver(new MyBeanResolver());

// This will end up calling resolve(context,"foo") on MyBeanResolver during evaluation

Object bean = parser.parseExpression("@foo").getValue(context);

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 186

Ternary Operator (If-Then-Else)

You can use the ternary operator for performing if-then-else conditional logic inside the expression. A

minimal example is:

String falseString = parser.parseExpression(

"false ? trueExp : falseExp").getValue(String.class);

In this case, the boolean false results in returning the string value falseExp. A more realistic example

is shown below.

parser.parseExpression("Name").setValue(societyContext, "IEEE");

societyContext.setVariable("queryName", "Nikola Tesla");

expression = "isMember(#queryName)? #queryName + ' is a member of the ' " +

"+ Name + ' Society' : #queryName + ' is not a member of the ' + Name + ' Society'";

String queryResultString = parser.parseExpression(expression)

.getValue(societyContext, String.class);

// queryResultString = "Nikola Tesla is a member of the IEEE Society"

Also see the next section on the Elvis operator for an even shorter syntax for the ternary operator.

The Elvis Operator

The Elvis operator is a shortening of the ternary operator syntax and is used in the Groovy language.

With the ternary operator syntax you usually have to repeat a variable twice, for example:

String name = "Elvis Presley";

String displayName = name != null ? name : "Unknown";

Instead you can use the Elvis operator, named for the resemblance to Elvis' hair style.

ExpressionParser parser = new SpelExpressionParser();

String name = parser.parseExpression("null?:'Unknown'").getValue(String.class);

System.out.println(name); // Unknown

Here is a more complex example.

ExpressionParser parser = new SpelExpressionParser();

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");

StandardEvaluationContext context = new StandardEvaluationContext(tesla);

String name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, String.class);

System.out.println(name); // Nikola Tesla

tesla.setName(null);

name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, String.class);

System.out.println(name); // Elvis Presley

Safe Navigation operator

The Safe Navigation operator is used to avoid a NullPointerException and comes from the Groovy

language. Typically when you have a reference to an object you might need to verify that it is not null

before accessing methods or properties of the object. To avoid this, the safe navigation operator will

simply return null instead of throwing an exception.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 187

ExpressionParser parser = new SpelExpressionParser();

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");

tesla.setPlaceOfBirth(new PlaceOfBirth("Smiljan"));

StandardEvaluationContext context = new StandardEvaluationContext(tesla);

String city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, String.class);

System.out.println(city); // Smiljan

tesla.setPlaceOfBirth(null);

city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, String.class);

System.out.println(city); // null - does not throw NullPointerException!!!

Note

The Elvis operator can be used to apply default values in expressions, e.g. in an @Value

expression:

@Value("#{systemProperties[pop3.port] ?: 25}")

This will inject a system property pop3.port if it is defined or 25 if not.

Collection Selection

Selection is a powerful expression language feature that allows you to transform some source collection

into another by selecting from its entries.

Selection uses the syntax ?[selectionExpression]. This will filter the collection and return a new

collection containing a subset of the original elements. For example, selection would allow us to easily

get a list of Serbian inventors:

List<Inventor> list = (List<Inventor>) parser.parseExpression(

"Members.?[Nationality == Serbian]").getValue(societyContext);

Selection is possible upon both lists and maps. In the former case the selection criteria is evaluated

against each individual list element whilst against a map the selection criteria is evaluated against each

map entry (objects of the Java type Map.Entry). Map entries have their key and value accessible as

properties for use in the selection.

This expression will return a new map consisting of those elements of the original map where the entry

value is less than 27.

Map newMap = parser.parseExpression("map.?[value<27]").getValue();

In addition to returning all the selected elements, it is possible to retrieve just the first or the last value.

To obtain the first entry matching the selection the syntax is ^[...] whilst to obtain the last matching

selection the syntax is $[...].

Collection Projection

Projection allows a collection to drive the evaluation of a sub-expression and the result is a new

collection. The syntax for projection is ![projectionExpression]. Most easily understood by

example, suppose we have a list of inventors but want the list of cities where they were born. Effectively

we want to evaluate placeOfBirth.city for every entry in the inventor list. Using projection:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 188

// returns [Smiljan, Idvor ]

List placesOfBirth = (List)parser.parseExpression("Members.![placeOfBirth.city]");

A map can also be used to drive projection and in this case the projection expression is evaluated

against each entry in the map (represented as a Java Map.Entry). The result of a projection across a

map is a list consisting of the evaluation of the projection expression against each map entry.

Expression templating

Expression templates allow a mixing of literal text with one or more evaluation blocks. Each evaluation

block is delimited with prefix and suffix characters that you can define, a common choice is to use #{ }

as the delimiters. For example,

String randomPhrase = parser.parseExpression(

"random number is #{T(java.lang.Math).random()}",

new TemplateParserContext()).getValue(String.class);

// evaluates to "random number is 0.7038186818312008"

The string is evaluated by concatenating the literal text 'random number is ' with the result of evaluating

the expression inside the #{ } delimiter, in this case the result of calling that random() method. The second

argument to the method parseExpression() is of the type ParserContext. The ParserContext

interface is used to influence how the expression is parsed in order to support the expression templating

functionality. The definition of TemplateParserContext is shown below.

public class TemplateParserContext implements ParserContext {

public String getExpressionPrefix() {

return "#{";

}

public String getExpressionSuffix() {

return "}";

}

public boolean isTemplate() {

return true;

}

8.6 Classes used in the examples

Inventor.java

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 189

package org.spring.samples.spel.inventor;

import java.util.Date;

import java.util.GregorianCalendar;

public class Inventor {

private String name;

private String nationality;

private String[] inventions;

private Date birthdate;

private PlaceOfBirth placeOfBirth;

public Inventor(String name, String nationality) {

GregorianCalendar c= new GregorianCalendar();

this.name = name;

this.nationality = nationality;

this.birthdate = c.getTime();

}

public Inventor(String name, Date birthdate, String nationality) {

this.name = name;

this.nationality = nationality;

this.birthdate = birthdate;

}

public Inventor() {

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getNationality() {

return nationality;

}

public void setNationality(String nationality) {

this.nationality = nationality;

}

public Date getBirthdate() {

return birthdate;

}

public void setBirthdate(Date birthdate) {

this.birthdate = birthdate;

}

public PlaceOfBirth getPlaceOfBirth() {

return placeOfBirth;

}

public void setPlaceOfBirth(PlaceOfBirth placeOfBirth) {

this.placeOfBirth = placeOfBirth;

}

public void setInventions(String[] inventions) {

this.inventions = inventions;

}

public String[] getInventions() {

return inventions;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 190

PlaceOfBirth.java

package org.spring.samples.spel.inventor;

public class PlaceOfBirth {

private String city;

private String country;

public PlaceOfBirth(String city) {

this.city=city;

}

public PlaceOfBirth(String city, String country) {

this(city);

this.country = country;

}

public String getCity() {

return city;

}

public void setCity(String s) {

this.city = s;

}

public String getCountry() {

return country;

}

public void setCountry(String country) {

this.country = country;

}

Society.java

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 191

package org.spring.samples.spel.inventor;

import java.util.*;

public class Society {

private String name;

public static String Advisors = "advisors";

public static String President = "president";

private List<Inventor> members = new ArrayList<Inventor>();

private Map officers = new HashMap();

public List getMembers() {

return members;

}

public Map getOfficers() {

return officers;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public boolean isMember(String name) {

for (Inventor inventor : members) {

if (inventor.getName().equals(name)) {

return true;

}

return false;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 192

9. Aspect Oriented Programming with Spring

9.1 Introduction

Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing

another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas

in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns such as

transaction management that cut across multiple types and objects. (Such concerns are often termed

crosscutting concerns in AOP literature.)

One of the key components of Spring is the AOP framework. While the Spring IoC container does not

depend on AOP, meaning you do not need to use AOP if you don’t want to, AOP complements Spring

IoC to provide a very capable middleware solution.

Spring 2.0 AOP

Spring 2.0 introduces a simpler and more powerful way of writing custom aspects using either a

schema-based approach or the @AspectJ annotation style. Both of these styles offer fully typed

advice and use of the AspectJ pointcut language, while still using Spring AOP for weaving.

The Spring 2.0 schema- and @AspectJ-based AOP support is discussed in this chapter. Spring 2.0

AOP remains fully backwards compatible with Spring 1.2 AOP, and the lower-level AOP support

offered by the Spring 1.2 APIs is discussed in the following chapter.

AOP is used in the Spring Framework to…

• … provide declarative enterprise services, especially as a replacement for EJB declarative services.

The most important such service is declarative transaction management.

• … allow users to implement custom aspects, complementing their use of OOP with AOP.

Note

If you are interested only in generic declarative services or other pre-packaged declarative

middleware services such as pooling, you do not need to work directly with Spring AOP, and can

skip most of this chapter.

AOP concepts

Let us begin by defining some central AOP concepts and terminology. These terms are not Spring-

specific… unfortunately, AOP terminology is not particularly intuitive; however, it would be even more

confusing if Spring used its own terminology.

•Aspect: a modularization of a concern that cuts across multiple classes. Transaction management is

a good example of a crosscutting concern in enterprise Java applications. In Spring AOP, aspects

are implemented using regular classes (the schema-based approach) or regular classes annotated

with the @Aspect annotation (the @AspectJ style).

•Join point: a point during the execution of a program, such as the execution of a method or the handling

of an exception. In Spring AOP, a join point always represents a method execution.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 193

•Advice: action taken by an aspect at a particular join point. Different types of advice include "around,"

"before" and "after" advice. (Advice types are discussed below.) Many AOP frameworks, including

Spring, model an advice as an interceptor, maintaining a chain of interceptors around the join point.

•Pointcut: a predicate that matches join points. Advice is associated with a pointcut expression and

runs at any join point matched by the pointcut (for example, the execution of a method with a certain

name). The concept of join points as matched by pointcut expressions is central to AOP, and Spring

uses the AspectJ pointcut expression language by default.

•Introduction: declaring additional methods or fields on behalf of a type. Spring AOP allows you to

introduce new interfaces (and a corresponding implementation) to any advised object. For example,

you could use an introduction to make a bean implement an IsModified interface, to simplify

caching. (An introduction is known as an inter-type declaration in the AspectJ community.)

•Target object: object being advised by one or more aspects. Also referred to as the advised object.

Since Spring AOP is implemented using runtime proxies, this object will always be a proxied object.

•AOP proxy: an object created by the AOP framework in order to implement the aspect contracts

(advise method executions and so on). In the Spring Framework, an AOP proxy will be a JDK dynamic

proxy or a CGLIB proxy.

•Weaving: linking aspects with other application types or objects to create an advised object. This can

be done at compile time (using the AspectJ compiler, for example), load time, or at runtime. Spring

AOP, like other pure Java AOP frameworks, performs weaving at runtime.

Types of advice:

•Before advice: Advice that executes before a join point, but which does not have the ability to prevent

execution flow proceeding to the join point (unless it throws an exception).

•After returning advice: Advice to be executed after a join point completes normally: for example, if a

method returns without throwing an exception.

•After throwing advice: Advice to be executed if a method exits by throwing an exception.

•After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal

or exceptional return).

•Around advice: Advice that surrounds a join point such as a method invocation. This is the most

powerful kind of advice. Around advice can perform custom behavior before and after the method

invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the

advised method execution by returning its own return value or throwing an exception.

Around advice is the most general kind of advice. Since Spring AOP, like AspectJ, provides a full range

of advice types, we recommend that you use the least powerful advice type that can implement the

required behavior. For example, if you need only to update a cache with the return value of a method, you

are better off implementing an after returning advice than an around advice, although an around advice

can accomplish the same thing. Using the most specific advice type provides a simpler programming

model with less potential for errors. For example, you do not need to invoke the proceed() method on

the JoinPoint used for around advice, and hence cannot fail to invoke it.

In Spring 2.0, all advice parameters are statically typed, so that you work with advice parameters of

the appropriate type (the type of the return value from a method execution for example) rather than

Object arrays.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 194

The concept of join points, matched by pointcuts, is the key to AOP which distinguishes it from

older technologies offering only interception. Pointcuts enable advice to be targeted independently

of the Object-Oriented hierarchy. For example, an around advice providing declarative transaction

management can be applied to a set of methods spanning multiple objects (such as all business

operations in the service layer).

Spring AOP capabilities and goals

Spring AOP is implemented in pure Java. There is no need for a special compilation process. Spring AOP

does not need to control the class loader hierarchy, and is thus suitable for use in a Servlet container

or application server.

Spring AOP currently supports only method execution join points (advising the execution of methods

on Spring beans). Field interception is not implemented, although support for field interception could be

added without breaking the core Spring AOP APIs. If you need to advise field access and update join

points, consider a language such as AspectJ.

Spring AOP’s approach to AOP differs from that of most other AOP frameworks. The aim is not to provide

the most complete AOP implementation (although Spring AOP is quite capable); it is rather to provide

a close integration between AOP implementation and Spring IoC to help solve common problems in

enterprise applications.

Thus, for example, the Spring Framework’s AOP functionality is normally used in conjunction with the

Spring IoC container. Aspects are configured using normal bean definition syntax (although this allows

powerful "autoproxying" capabilities): this is a crucial difference from other AOP implementations. There

are some things you cannot do easily or efficiently with Spring AOP, such as advise very fine-grained

objects (such as domain objects typically): AspectJ is the best choice in such cases. However, our

experience is that Spring AOP provides an excellent solution to most problems in enterprise Java

applications that are amenable to AOP.

Spring AOP will never strive to compete with AspectJ to provide a comprehensive AOP solution. We

believe that both proxy-based frameworks like Spring AOP and full-blown frameworks such as AspectJ

are valuable, and that they are complementary, rather than in competition. Spring seamlessly integrates

Spring AOP and IoC with AspectJ, to enable all uses of AOP to be catered for within a consistent Spring-

based application architecture. This integration does not affect the Spring AOP API or the AOP Alliance

API: Spring AOP remains backward-compatible. See the following chapter for a discussion of the Spring

AOP APIs.

Note

One of the central tenets of the Spring Framework is that of non-invasiveness; this is the idea

that you should not be forced to introduce framework-specific classes and interfaces into your

business/domain model. However, in some places the Spring Framework does give you the option

to introduce Spring Framework-specific dependencies into your codebase: the rationale in giving

you such options is because in certain scenarios it might be just plain easier to read or code some

specific piece of functionality in such a way. The Spring Framework (almost) always offers you

the choice though: you have the freedom to make an informed decision as to which option best

suits your particular use case or scenario.

One such choice that is relevant to this chapter is that of which AOP framework (and which AOP

style) to choose. You have the choice of AspectJ and/or Spring AOP, and you also have the choice

of either the @AspectJ annotation-style approach or the Spring XML configuration-style approach.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 195

The fact that this chapter chooses to introduce the @AspectJ-style approach first should not be

taken as an indication that the Spring team favors the @AspectJ annotation-style approach over

the Spring XML configuration-style.

See Section 9.4, “Choosing which AOP declaration style to use” for a more complete discussion

of the whys and wherefores of each style.

AOP Proxies

Spring AOP defaults to using standard JDK dynamic proxies for AOP proxies. This enables any interface

(or set of interfaces) to be proxied.

Spring AOP can also use CGLIB proxies. This is necessary to proxy classes, rather than interfaces.

CGLIB is used by default if a business object does not implement an interface. As it is good practice

to program to interfaces rather than classes, business classes normally will implement one or more

business interfaces. It is possible to force the use of CGLIB, in those (hopefully rare) cases where you

need to advise a method that is not declared on an interface, or where you need to pass a proxied object

to a method as a concrete type.

It is important to grasp the fact that Spring AOP is proxy-based. See the section called “Understanding

AOP proxies” for a thorough examination of exactly what this implementation detail actually means.

9.2 @AspectJ support

@AspectJ refers to a style of declaring aspects as regular Java classes annotated with annotations.

The @AspectJ style was introduced by the AspectJ project as part of the AspectJ 5 release. Spring

interprets the same annotations as AspectJ 5, using a library supplied by AspectJ for pointcut parsing

and matching. The AOP runtime is still pure Spring AOP though, and there is no dependency on the

AspectJ compiler or weaver.

Note

Using the AspectJ compiler and weaver enables use of the full AspectJ language, and is discussed

in Section 9.8, “Using AspectJ with Spring applications”.

Enabling @AspectJ Support

To use @AspectJ aspects in a Spring configuration you need to enable Spring support for configuring

Spring AOP based on @AspectJ aspects, and autoproxying beans based on whether or not they are

advised by those aspects. By autoproxying we mean that if Spring determines that a bean is advised by

one or more aspects, it will automatically generate a proxy for that bean to intercept method invocations

and ensure that advice is executed as needed.

The @AspectJ support can be enabled with XML or Java style configuration. In either case you will

also need to ensure that AspectJ’s aspectjweaver.jar library is on the classpath of your application

(version 1.6.8 or later). This library is available in the 'lib' directory of an AspectJ distribution or via

the Maven Central repository.

Enabling @AspectJ Support with Java configuration

To enable @AspectJ support with Java @Configuration add the @EnableAspectJAutoProxy

annotation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 196

@Configuration

@EnableAspectJAutoProxy

public class AppConfig {

}

Enabling @AspectJ Support with XML configuration

To enable @AspectJ support with XML based configuration use the aop:aspectj-autoproxy

element:

<aop:aspectj-autoproxy/>

This assumes that you are using schema support as described in Chapter 34, XML Schema-based

configuration. See the section called “the aop schema” for how to import the tags in the aop namespace.

Declaring an aspect

With the @AspectJ support enabled, any bean defined in your application context with a class that is

an @AspectJ aspect (has the @Aspect annotation) will be automatically detected by Spring and used

to configure Spring AOP. The following example shows the minimal definition required for a not-very-

useful aspect:

A regular bean definition in the application context, pointing to a bean class that has the @Aspect

annotation:

</bean>

And the NotVeryUsefulAspect class definition, annotated with

org.aspectj.lang.annotation.Aspect annotation;

package org.xyz;

import org.aspectj.lang.annotation.Aspect;

@Aspect

public class NotVeryUsefulAspect {

}

Aspects (classes annotated with @Aspect) may have methods and fields just like any other class. They

may also contain pointcut, advice, and introduction (inter-type) declarations.

Autodetecting aspects through component scanning

You may register aspect classes as regular beans in your Spring XML configuration, or autodetect

them through classpath scanning - just like any other Spring-managed bean. However, note that

the @Aspect annotation is not sufficient for autodetection in the classpath: For that purpose, you

need to add a separate @Component annotation (or alternatively a custom stereotype annotation

that qualifies, as per the rules of Spring’s component scanner).

Advising aspects with other aspects?

In Spring AOP, it is not possible to have aspects themselves be the target of advice from other

aspects. The @Aspect annotation on a class marks it as an aspect, and hence excludes it from

auto-proxying.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 197

Declaring a pointcut

Recall that pointcuts determine join points of interest, and thus enable us to control when advice

executes. Spring AOP only supports method execution join points for Spring beans, so you can think of

a pointcut as matching the execution of methods on Spring beans. A pointcut declaration has two parts:

a signature comprising a name and any parameters, and a pointcut expression that determines exactly

which method executions we are interested in. In the @AspectJ annotation-style of AOP, a pointcut

signature is provided by a regular method definition, and the pointcut expression is indicated using the

@Pointcut annotation (the method serving as the pointcut signature must have a void return type).

An example will help make this distinction between a pointcut signature and a pointcut expression clear.

The following example defines a pointcut named 'anyOldTransfer' that will match the execution of

any method named 'transfer':

@Pointcut("execution(* transfer(..))")// the pointcut expression

private void anyOldTransfer() {}// the pointcut signature

The pointcut expression that forms the value of the @Pointcut annotation is a regular AspectJ 5

pointcut expression. For a full discussion of AspectJ’s pointcut language, see the AspectJ Programming

Guide (and for extensions, the AspectJ 5 Developers Notebook) or one of the books on AspectJ such

as "Eclipse AspectJ" by Colyer et. al. or "AspectJ in Action" by Ramnivas Laddad.

Supported Pointcut Designators

Spring AOP supports the following AspectJ pointcut designators (PCD) for use in pointcut expressions:

Other pointcut types

The full AspectJ pointcut language supports additional pointcut designators that are not supported

in Spring. These are: call, get, set, preinitialization, staticinitialization,

initialization, handler, adviceexecution, withincode, cflow, cflowbelow,

if, @this, and @withincode. Use of these pointcut designators in pointcut expressions

interpreted by Spring AOP will result in an IllegalArgumentException being thrown.

The set of pointcut designators supported by Spring AOP may be extended in future releases to

support more of the AspectJ pointcut designators.

•execution - for matching method execution join points, this is the primary pointcut designator you will

use when working with Spring AOP

•within - limits matching to join points within certain types (simply the execution of a method declared

within a matching type when using Spring AOP)

•this - limits matching to join points (the execution of methods when using Spring AOP) where the bean

reference (Spring AOP proxy) is an instance of the given type

•target - limits matching to join points (the execution of methods when using Spring AOP) where the

target object (application object being proxied) is an instance of the given type

•args - limits matching to join points (the execution of methods when using Spring AOP) where the

arguments are instances of the given types

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 198

•@target - limits matching to join points (the execution of methods when using Spring AOP) where the

class of the executing object has an annotation of the given type

•@args - limits matching to join points (the execution of methods when using Spring AOP) where the

runtime type of the actual arguments passed have annotations of the given type(s)

•@within - limits matching to join points within types that have the given annotation (the execution of

methods declared in types with the given annotation when using Spring AOP)

•@annotation - limits matching to join points where the subject of the join point (method being executed

in Spring AOP) has the given annotation

Because Spring AOP limits matching to only method execution join points, the discussion of the pointcut

designators above gives a narrower definition than you will find in the AspectJ programming guide. In

addition, AspectJ itself has type-based semantics and at an execution join point both this and target

refer to the same object - the object executing the method. Spring AOP is a proxy-based system and

differentiates between the proxy object itself (bound to this) and the target object behind the proxy

(bound to target).

Note

Due to the proxy-based nature of Spring’s AOP framework, protected methods are by definition

not intercepted, neither for JDK proxies (where this isn’t applicable) nor for CGLIB proxies (where

this is technically possible but not recommendable for AOP purposes). As a consequence, any

given pointcut will be matched against public methods only!

If your interception needs include protected/private methods or even constructors, consider the

use of Spring-driven native AspectJ weaving instead of Spring’s proxy-based AOP framework.

This constitutes a different mode of AOP usage with different characteristics, so be sure to make

yourself familiar with weaving first before making a decision.

Spring AOP also supports an additional PCD named bean. This PCD allows you to limit the matching of

join points to a particular named Spring bean, or to a set of named Spring beans (when using wildcards).

The bean PCD has the following form:

bean(idOrNameOfBean)

The idOrNameOfBean token can be the name of any Spring bean: limited wildcard support using the *

character is provided, so if you establish some naming conventions for your Spring beans you can quite

easily write a bean PCD expression to pick them out. As is the case with other pointcut designators,

the bean PCD can be &&'ed, ||'ed, and ! (negated) too.

Note

Please note that the bean PCD is only supported in Spring AOP - and not in native AspectJ

weaving. It is a Spring-specific extension to the standard PCDs that AspectJ defines.

The bean PCD operates at the instance level (building on the Spring bean name concept) rather

than at the type level only (which is what weaving-based AOP is limited to). Instance-based

pointcut designators are a special capability of Spring’s proxy-based AOP framework and its close

integration with the Spring bean factory, where it is natural and straightforward to identify specific

beans by name.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 199

Combining pointcut expressions

Pointcut expressions can be combined using &&, || and !. It is also possible to refer

to pointcut expressions by name. The following example shows three pointcut expressions:

anyPublicOperation (which matches if a method execution join point represents the execution of

any public method); inTrading (which matches if a method execution is in the trading module), and

tradingOperation (which matches if a method execution represents any public method in the trading

module).

@Pointcut("execution(public * (..))")

private void anyPublicOperation() {}

@Pointcut("within(com.xyz.someapp.trading..)")

private void inTrading() {}

@Pointcut("anyPublicOperation() && inTrading()")

private void tradingOperation() {}

It is a best practice to build more complex pointcut expressions out of smaller named components as

shown above. When referring to pointcuts by name, normal Java visibility rules apply (you can see

private pointcuts in the same type, protected pointcuts in the hierarchy, public pointcuts anywhere and

so on). Visibility does not affect pointcut matching.

Sharing common pointcut definitions

When working with enterprise applications, you often want to refer to modules of the application

and particular sets of operations from within several aspects. We recommend defining a

"SystemArchitecture" aspect that captures common pointcut expressions for this purpose. A typical such

aspect would look as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 200

package com.xyz.someapp;

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Pointcut;

@Aspect

public class SystemArchitecture {

* A join point is in the web layer if the method is defined

* in a type in the com.xyz.someapp.web package or any sub-package

* under that.

@Pointcut("within(com.xyz.someapp.web..)")

public void inWebLayer() {}

* A join point is in the service layer if the method is defined

* in a type in the com.xyz.someapp.service package or any sub-package

* under that.

@Pointcut("within(com.xyz.someapp.service..)")

public void inServiceLayer() {}

* A join point is in the data access layer if the method is defined

* in a type in the com.xyz.someapp.dao package or any sub-package

* under that.

@Pointcut("within(com.xyz.someapp.dao..)")

public void inDataAccessLayer() {}

* A business service is the execution of any method defined on a service

* interface. This definition assumes that interfaces are placed in the

* "service" package, and that implementation types are in sub-packages.

* If you group service interfaces by functional area (for example,

* in packages com.xyz.someapp.abc.service and com.xyz.someapp.def.service) then

* the pointcut expression "execution(* com.xyz.someapp..service..(..))"

* could be used instead.

* Alternatively, you can write the expression using the bean

* PCD, like so "bean(Service)". (This assumes that you have

* named your Spring service beans in a consistent fashion.)

@Pointcut("execution( com.xyz.someapp..service..(..))")

public void businessService() {}

* A data access operation is the execution of any method defined on a

* dao interface. This definition assumes that interfaces are placed in the

* "dao" package, and that implementation types are in sub-packages.

@Pointcut("execution( com.xyz.someapp.dao..(..))")

public void dataAccessOperation() {}

}

The pointcuts defined in such an aspect can be referred to anywhere that you need a pointcut

expression. For example, to make the service layer transactional, you could write:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 201

<aop:config>

<aop:advisor

pointcut="com.xyz.someapp.SystemArchitecture.businessService()"

advice-ref="tx-advice"/>

</aop:config>

<tx:advice id="tx-advice">

<tx:attributes>

<tx:method name="*" propagation="REQUIRED"/>

</tx:attributes>

</tx:advice>

The <aop:config> and <aop:advisor> elements are discussed in Section 9.3, “Schema-based

AOP support”. The transaction elements are discussed in Chapter 12, Transaction Management.

Examples

Spring AOP users are likely to use the execution pointcut designator the most often. The format of

an execution expression is:

execution(modifiers-pattern? ret-type-pattern declaring-type-pattern? name-pattern(param-pattern)

throws-pattern?)

All parts except the returning type pattern (ret-type-pattern in the snippet above), name pattern, and

parameters pattern are optional. The returning type pattern determines what the return type of the

method must be in order for a join point to be matched. Most frequently you will use * as the returning

type pattern, which matches any return type. A fully-qualified type name will match only when the method

returns the given type. The name pattern matches the method name. You can use the * wildcard as all

or part of a name pattern. The parameters pattern is slightly more complex: () matches a method that

takes no parameters, whereas (..) matches any number of parameters (zero or more). The pattern

(*) matches a method taking one parameter of any type, (*,String) matches a method taking two

parameters, the first can be of any type, the second must be a String. Consult the Language Semantics

section of the AspectJ Programming Guide for more information.

Some examples of common pointcut expressions are given below.

• the execution of any public method:

execution(public * *(..))

• the execution of any method with a name beginning with "set":

execution(* set*(..))

• the execution of any method defined by the AccountService interface:

execution(* com.xyz.service.AccountService.*(..))

• the execution of any method defined in the service package:

execution(* com.xyz.service..(..))

• the execution of any method defined in the service package or a sub-package:

execution(* com.xyz.service...(..))

• any join point (method execution only in Spring AOP) within the service package:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 202

within(com.xyz.service.*)

• any join point (method execution only in Spring AOP) within the service package or a sub-package:

within(com.xyz.service..*)

• any join point (method execution only in Spring AOP) where the proxy implements the

AccountService interface:

this(com.xyz.service.AccountService)

Note

this is more commonly used in a binding form :- see the following section on advice for how to

make the proxy object available in the advice body.

• any join point (method execution only in Spring AOP) where the target object implements the

AccountService interface:

target(com.xyz.service.AccountService)

Note

target is more commonly used in a binding form :- see the following section on advice for how to

make the target object available in the advice body.

• any join point (method execution only in Spring AOP) which takes a single parameter, and where the

argument passed at runtime is Serializable:

args(java.io.Serializable)

Note

args is more commonly used in a binding form :- see the following section on advice for how to

make the method arguments available in the advice body.

Note that the pointcut given in this example is different to execution(*

*(java.io.Serializable)): the args version matches if the argument passed at runtime is

Serializable, the execution version matches if the method signature declares a single parameter of type

Serializable.

• any join point (method execution only in Spring AOP) where the target object has an

@Transactional annotation:

@target(org.springframework.transaction.annotation.Transactional)

Note

@target can also be used in a binding form :- see the following section on advice for how to make

the annotation object available in the advice body.

• any join point (method execution only in Spring AOP) where the declared type of the target object

has an @Transactional annotation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 203

@within(org.springframework.transaction.annotation.Transactional)

Note

@within can also be used in a binding form :- see the following section on advice for how to make

the annotation object available in the advice body.

• any join point (method execution only in Spring AOP) where the executing method has an

@Transactional annotation:

@annotation(org.springframework.transaction.annotation.Transactional)

Note

@annotation can also be used in a binding form :- see the following section on advice for how to

make the annotation object available in the advice body.

• any join point (method execution only in Spring AOP) which takes a single parameter, and where the

runtime type of the argument passed has the @Classified annotation:

@args(com.xyz.security.Classified)

Note

@args can also be used in a binding form :- see the following section on advice for how to make

the annotation object(s) available in the advice body.

• any join point (method execution only in Spring AOP) on a Spring bean named tradeService:

bean(tradeService)

• any join point (method execution only in Spring AOP) on Spring beans having names that match the

wildcard expression *Service:

bean(*Service)

Writing good pointcuts

During compilation, AspectJ processes pointcuts in order to try and optimize matching performance.

Examining code and determining if each join point matches (statically or dynamically) a given pointcut

is a costly process. (A dynamic match means the match cannot be fully determined from static analysis

and a test will be placed in the code to determine if there is an actual match when the code is running).

On first encountering a pointcut declaration, AspectJ will rewrite it into an optimal form for the matching

process. What does this mean? Basically pointcuts are rewritten in DNF (Disjunctive Normal Form) and

the components of the pointcut are sorted such that those components that are cheaper to evaluate are

checked first. This means you do not have to worry about understanding the performance of various

pointcut designators and may supply them in any order in a pointcut declaration.

However, AspectJ can only work with what it is told, and for optimal performance of matching you

should think about what they are trying to achieve and narrow the search space for matches as much

as possible in the definition. The existing designators naturally fall into one of three groups: kinded,

scoping and context:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 204

• Kinded designators are those which select a particular kind of join point. For example: execution, get,

set, call, handler

• Scoping designators are those which select a group of join points of interest (of probably many kinds).

For example: within, withincode

• Contextual designators are those that match (and optionally bind) based on context. For example:

this, target, @annotation

A well written pointcut should try and include at least the first two types (kinded and scoping), whilst

the contextual designators may be included if wishing to match based on join point context, or bind that

context for use in the advice. Supplying either just a kinded designator or just a contextual designator will

work but could affect weaving performance (time and memory used) due to all the extra processing and

analysis. Scoping designators are very fast to match and their usage means AspectJ can very quickly

dismiss groups of join points that should not be further processed - that is why a good pointcut should

always include one if possible.

Declaring advice

Advice is associated with a pointcut expression, and runs before, after, or around method executions

matched by the pointcut. The pointcut expression may be either a simple reference to a named pointcut,

or a pointcut expression declared in place.

Before advice

Before advice is declared in an aspect using the @Before annotation:

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Before;

@Aspect

public class BeforeExample {

@Before("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")

public void doAccessCheck() {

// ...

}

If using an in-place pointcut expression we could rewrite the above example as:

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Before;

@Aspect

public class BeforeExample {

@Before("execution(* com.xyz.myapp.dao..(..))")

public void doAccessCheck() {

// ...

}

After returning advice

After returning advice runs when a matched method execution returns normally. It is declared using the

@AfterReturning annotation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 205

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.AfterReturning;

@Aspect

public class AfterReturningExample {

@AfterReturning("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")

public void doAccessCheck() {

// ...

}

Note

Note: it is of course possible to have multiple advice declarations, and other members as well,

all inside the same aspect. We’re just showing a single advice declaration in these examples to

focus on the issue under discussion at the time.

Sometimes you need access in the advice body to the actual value that was returned. You can use the

form of @AfterReturning that binds the return value for this:

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.AfterReturning;

@Aspect

public class AfterReturningExample {

@AfterReturning(

pointcut="com.xyz.myapp.SystemArchitecture.dataAccessOperation()",

returning="retVal")

public void doAccessCheck(Object retVal) {

// ...

}

The name used in the returning attribute must correspond to the name of a parameter in the advice

method. When a method execution returns, the return value will be passed to the advice method as

the corresponding argument value. A returning clause also restricts matching to only those method

executions that return a value of the specified type ( Object in this case, which will match any return

value).

Please note that it is not possible to return a totally different reference when using after-returning advice.

After throwing advice

After throwing advice runs when a matched method execution exits by throwing an exception. It is

declared using the @AfterThrowing annotation:

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.AfterThrowing;

@Aspect

public class AfterThrowingExample {

@AfterThrowing("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")

public void doRecoveryActions() {

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 206

Often you want the advice to run only when exceptions of a given type are thrown, and you also often

need access to the thrown exception in the advice body. Use the throwing attribute to both restrict

matching (if desired, use Throwable as the exception type otherwise) and bind the thrown exception

to an advice parameter.

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.AfterThrowing;

@Aspect

public class AfterThrowingExample {

@AfterThrowing(

pointcut="com.xyz.myapp.SystemArchitecture.dataAccessOperation()",

throwing="ex")

public void doRecoveryActions(DataAccessException ex) {

// ...

}

The name used in the throwing attribute must correspond to the name of a parameter in the advice

method. When a method execution exits by throwing an exception, the exception will be passed to the

advice method as the corresponding argument value. A throwing clause also restricts matching to

only those method executions that throw an exception of the specified type ( DataAccessException

in this case).

After (finally) advice

After (finally) advice runs however a matched method execution exits. It is declared using the @After

annotation. After advice must be prepared to handle both normal and exception return conditions. It is

typically used for releasing resources, etc.

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.After;

@Aspect

public class AfterFinallyExample {

@After("com.xyz.myapp.SystemArchitecture.dataAccessOperation()")

public void doReleaseLock() {

// ...

}

Around advice

The final kind of advice is around advice. Around advice runs "around" a matched method execution.

It has the opportunity to do work both before and after the method executes, and to determine when,

how, and even if, the method actually gets to execute at all. Around advice is often used if you need to

share state before and after a method execution in a thread-safe manner (starting and stopping a timer

for example). Always use the least powerful form of advice that meets your requirements (i.e. don’t use

around advice if simple before advice would do).

Around advice is declared using the @Around annotation. The first parameter of the advice method

must be of type ProceedingJoinPoint. Within the body of the advice, calling proceed() on the

ProceedingJoinPoint causes the underlying method to execute. The proceed method may also

be called passing in an Object[] - the values in the array will be used as the arguments to the method

execution when it proceeds.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 207

Note

The behavior of proceed when called with an Object[] is a little different than the behavior of

proceed for around advice compiled by the AspectJ compiler. For around advice written using

the traditional AspectJ language, the number of arguments passed to proceed must match the

number of arguments passed to the around advice (not the number of arguments taken by the

underlying join point), and the value passed to proceed in a given argument position supplants

the original value at the join point for the entity the value was bound to (Don’t worry if this doesn’t

make sense right now!). The approach taken by Spring is simpler and a better match to its proxy-

based, execution only semantics. You only need to be aware of this difference if you are compiling

@AspectJ aspects written for Spring and using proceed with arguments with the AspectJ compiler

and weaver. There is a way to write such aspects that is 100% compatible across both Spring

AOP and AspectJ, and this is discussed in the following section on advice parameters.

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Around;

import org.aspectj.lang.ProceedingJoinPoint;

@Aspect

public class AroundExample {

@Around("com.xyz.myapp.SystemArchitecture.businessService()")

public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable {

// start stopwatch

Object retVal = pjp.proceed();

// stop stopwatch

return retVal;

}

The value returned by the around advice will be the return value seen by the caller of the method. A

simple caching aspect for example could return a value from a cache if it has one, and invoke proceed()

if it does not. Note that proceed may be invoked once, many times, or not at all within the body of the

around advice, all of these are quite legal.

Advice parameters

Spring offers fully typed advice - meaning that you declare the parameters you need in the advice

signature (as we saw for the returning and throwing examples above) rather than work with Object[]

arrays all the time. We’ll see how to make argument and other contextual values available to the advice

body in a moment. First let’s take a look at how to write generic advice that can find out about the method

the advice is currently advising.

Access to the current JoinPoint

Any advice method may declare as its first parameter, a parameter of type

org.aspectj.lang.JoinPoint (please note that around advice is required to declare a first

parameter of type ProceedingJoinPoint, which is a subclass of JoinPoint. The JoinPoint

interface provides a number of useful methods such as getArgs() (returns the method arguments),

getThis() (returns the proxy object), getTarget() (returns the target object), getSignature()

(returns a description of the method that is being advised) and toString() (prints a useful description

of the method being advised). Please do consult the javadocs for full details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 208

Passing parameters to advice

We’ve already seen how to bind the returned value or exception value (using after returning and after

throwing advice). To make argument values available to the advice body, you can use the binding form

of args. If a parameter name is used in place of a type name in an args expression, then the value

of the corresponding argument will be passed as the parameter value when the advice is invoked. An

example should make this clearer. Suppose you want to advise the execution of dao operations that

take an Account object as the first parameter, and you need access to the account in the advice body.

You could write the following:

@Before("com.xyz.myapp.SystemArchitecture.dataAccessOperation() && args(account,..)")

public void validateAccount(Account account) {

// ...

}

The args(account,..) part of the pointcut expression serves two purposes: firstly, it restricts

matching to only those method executions where the method takes at least one parameter, and the

argument passed to that parameter is an instance of Account; secondly, it makes the actual Account

object available to the advice via the account parameter.

Another way of writing this is to declare a pointcut that "provides" the Account object value when it

matches a join point, and then just refer to the named pointcut from the advice. This would look as

follows:

@Pointcut("com.xyz.myapp.SystemArchitecture.dataAccessOperation() && args(account,..)")

private void accountDataAccessOperation(Account account) {}

@Before("accountDataAccessOperation(account)")

public void validateAccount(Account account) {

// ...

}

The interested reader is once more referred to the AspectJ programming guide for more details.

The proxy object ( this), target object ( target), and annotations ( @within, @target,

@annotation, @args) can all be bound in a similar fashion. The following example shows how you

could match the execution of methods annotated with an @Auditable annotation, and extract the audit

code.

First the definition of the @Auditable annotation:

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.METHOD)

public @interface Auditable {

AuditCode value();

}

And then the advice that matches the execution of @Auditable methods:

@Before("com.xyz.lib.Pointcuts.anyPublicMethod() && @annotation(auditable)")

public void audit(Auditable auditable) {

AuditCode code = auditable.value();

// ...

}

Advice parameters and generics

Spring AOP can handle generics used in class declarations and method parameters. Suppose you have

a generic type like this:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 209

public interface Sample<T> {

void sampleGenericMethod(T param);

void sampleGenericCollectionMethod(Collection>T> param);

}

You can restrict interception of method types to certain parameter types by simply typing the advice

parameter to the parameter type you want to intercept the method for:

@Before("execution(* ..Sample+.sampleGenericMethod(*)) && args(param)")

public void beforeSampleMethod(MyType param) {

// Advice implementation

}

That this works is pretty obvious as we already discussed above. However, it’s worth pointing out that

this won’t work for generic collections. So you cannot define a pointcut like this:

@Before("execution(* ..Sample+.sampleGenericCollectionMethod(*)) && args(param)")

public void beforeSampleMethod(Collection<MyType> param) {

// Advice implementation

}

To make this work we would have to inspect every element of the collection, which is not reasonable

as we also cannot decide how to treat null values in general. To achieve something similar to this you

have to type the parameter to Collection<?> and manually check the type of the elements.

Determining argument names

The parameter binding in advice invocations relies on matching names used in pointcut expressions

to declared parameter names in (advice and pointcut) method signatures. Parameter names are not

available through Java reflection, so Spring AOP uses the following strategies to determine parameter

names:

• If the parameter names have been specified by the user explicitly, then the specified parameter names

are used: both the advice and the pointcut annotations have an optional "argNames" attribute which

can be used to specify the argument names of the annotated method - these argument names are

available at runtime. For example:

@Before(value="com.xyz.lib.Pointcuts.anyPublicMethod() && target(bean) && @annotation(auditable)",

argNames="bean,auditable")

public void audit(Object bean, Auditable auditable) {

AuditCode code = auditable.value();

// ... use code and bean

}

If the first parameter is of the JoinPoint, ProceedingJoinPoint, or JoinPoint.StaticPart

type, you may leave out the name of the parameter from the value of the "argNames" attribute. For

example, if you modify the preceding advice to receive the join point object, the "argNames" attribute

need not include it:

@Before(value="com.xyz.lib.Pointcuts.anyPublicMethod() && target(bean) && @annotation(auditable)",

argNames="bean,auditable")

public void audit(JoinPoint jp, Object bean, Auditable auditable) {

AuditCode code = auditable.value();

// ... use code, bean, and jp

}

The special treatment given to the first parameter of the JoinPoint, ProceedingJoinPoint, and

JoinPoint.StaticPart types is particularly convenient for advice that do not collect any other join

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 210

point context. In such situations, you may simply omit the "argNames" attribute. For example, the

following advice need not declare the "argNames" attribute:

@Before("com.xyz.lib.Pointcuts.anyPublicMethod()")

public void audit(JoinPoint jp) {

// ... use jp

}

• Using the 'argNames' attribute is a little clumsy, so if the 'argNames' attribute has not been

specified, then Spring AOP will look at the debug information for the class and try to determine the

parameter names from the local variable table. This information will be present as long as the classes

have been compiled with debug information ( '-g:vars' at a minimum). The consequences of

compiling with this flag on are: (1) your code will be slightly easier to understand (reverse engineer), (2)

the class file sizes will be very slightly bigger (typically inconsequential), (3) the optimization to remove

unused local variables will not be applied by your compiler. In other words, you should encounter no

difficulties building with this flag on.

Note

If an @AspectJ aspect has been compiled by the AspectJ compiler (ajc) even without the debug

information then there is no need to add the argNames attribute as the compiler will retain the

needed information.

• If the code has been compiled without the necessary debug information, then Spring AOP will

attempt to deduce the pairing of binding variables to parameters (for example, if only one variable

is bound in the pointcut expression, and the advice method only takes one parameter, the pairing

is obvious!). If the binding of variables is ambiguous given the available information, then an

AmbiguousBindingException will be thrown.

• If all of the above strategies fail then an IllegalArgumentException will be thrown.

Proceeding with arguments

We remarked earlier that we would describe how to write a proceed call with arguments that works

consistently across Spring AOP and AspectJ. The solution is simply to ensure that the advice signature

binds each of the method parameters in order. For example:

@Around("execution(List<Account> find*(..)) && " +

"com.xyz.myapp.SystemArchitecture.inDataAccessLayer() && " +

"args(accountHolderNamePattern)")

public Object preProcessQueryPattern(ProceedingJoinPoint pjp,

String accountHolderNamePattern) throws Throwable {

String newPattern = preProcess(accountHolderNamePattern);

return pjp.proceed(new Object[] {newPattern});

}

In many cases you will be doing this binding anyway (as in the example above).

Advice ordering

What happens when multiple pieces of advice all want to run at the same join point? Spring AOP

follows the same precedence rules as AspectJ to determine the order of advice execution. The highest

precedence advice runs first "on the way in" (so given two pieces of before advice, the one with highest

precedence runs first). "On the way out" from a join point, the highest precedence advice runs last (so

given two pieces of after advice, the one with the highest precedence will run second).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 211

When two pieces of advice defined in different aspects both need to run at the same join point,

unless you specify otherwise the order of execution is undefined. You can control the order of

execution by specifying precedence. This is done in the normal Spring way by either implementing the

org.springframework.core.Ordered interface in the aspect class or annotating it with the Order

annotation. Given two aspects, the aspect returning the lower value from Ordered.getValue() (or

the annotation value) has the higher precedence.

When two pieces of advice defined in the same aspect both need to run at the same join point, the

ordering is undefined (since there is no way to retrieve the declaration order via reflection for javac-

compiled classes). Consider collapsing such advice methods into one advice method per join point in

each aspect class, or refactor the pieces of advice into separate aspect classes - which can be ordered

at the aspect level.

Introductions

Introductions (known as inter-type declarations in AspectJ) enable an aspect to declare that advised

objects implement a given interface, and to provide an implementation of that interface on behalf of

those objects.

An introduction is made using the @DeclareParents annotation. This annotation is used to

declare that matching types have a new parent (hence the name). For example, given an interface

UsageTracked, and an implementation of that interface DefaultUsageTracked, the following

aspect declares that all implementors of service interfaces also implement the UsageTracked interface.

(In order to expose statistics via JMX for example.)

@Aspect

public class UsageTracking {

@DeclareParents(value="com.xzy.myapp.service.*+", defaultImpl=DefaultUsageTracked.class)

public static UsageTracked mixin;

@Before("com.xyz.myapp.SystemArchitecture.businessService() && this(usageTracked)")

public void recordUsage(UsageTracked usageTracked) {

usageTracked.incrementUseCount();

}

The interface to be implemented is determined by the type of the annotated field. The value attribute

of the @DeclareParents annotation is an AspectJ type pattern :- any bean of a matching type will

implement the UsageTracked interface. Note that in the before advice of the above example, service

beans can be directly used as implementations of the UsageTracked interface. If accessing a bean

programmatically you would write the following:

UsageTracked usageTracked = (UsageTracked) context.getBean("myService");

Aspect instantiation models

Note

(This is an advanced topic, so if you are just starting out with AOP you can safely skip it until later.)

By default there will be a single instance of each aspect within the application context. AspectJ calls

this the singleton instantiation model. It is possible to define aspects with alternate lifecycles :- Spring

supports AspectJ’s perthis and pertarget instantiation models ( percflow, percflowbelow,

and pertypewithin are not currently supported).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 212

A "perthis" aspect is declared by specifying a perthis clause in the @Aspect annotation. Let’s look

at an example, and then we’ll explain how it works.

@Aspect("perthis(com.xyz.myapp.SystemArchitecture.businessService())")

public class MyAspect {

private int someState;

@Before(com.xyz.myapp.SystemArchitecture.businessService())

public void recordServiceUsage() {

// ...

}

The effect of the 'perthis' clause is that one aspect instance will be created for each unique service

object executing a business service (each unique object bound to this at join points matched by the

pointcut expression). The aspect instance is created the first time that a method is invoked on the service

object. The aspect goes out of scope when the service object goes out of scope. Before the aspect

instance is created, none of the advice within it executes. As soon as the aspect instance has been

created, the advice declared within it will execute at matched join points, but only when the service object

is the one this aspect is associated with. See the AspectJ programming guide for more information on

per-clauses.

The 'pertarget' instantiation model works in exactly the same way as perthis, but creates one aspect

instance for each unique target object at matched join points.

Example

Now that you have seen how all the constituent parts work, let’s put them together to do something

useful!

The execution of business services can sometimes fail due to concurrency issues (for example, deadlock

loser). If the operation is retried, it is quite likely to succeed next time round. For business services

where it is appropriate to retry in such conditions (idempotent operations that don’t need to go back to

the user for conflict resolution), we’d like to transparently retry the operation to avoid the client seeing

a PessimisticLockingFailureException. This is a requirement that clearly cuts across multiple

services in the service layer, and hence is ideal for implementing via an aspect.

Because we want to retry the operation, we will need to use around advice so that we can call proceed

multiple times. Here’s how the basic aspect implementation looks:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 213

@Aspect

public class ConcurrentOperationExecutor implements Ordered {

private static final int DEFAULT_MAX_RETRIES = 2;

private int maxRetries = DEFAULT_MAX_RETRIES;

private int order = 1;

public void setMaxRetries(int maxRetries) {

this.maxRetries = maxRetries;

}

public int getOrder() {

return this.order;

}

public void setOrder(int order) {

this.order = order;

}

@Around("com.xyz.myapp.SystemArchitecture.businessService()")

public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {

int numAttempts = 0;

PessimisticLockingFailureException lockFailureException;

do {

numAttempts++;

try {

return pjp.proceed();

}

catch(PessimisticLockingFailureException ex) {

lockFailureException = ex;

}

} while(numAttempts <= this.maxRetries);

throw lockFailureException;

}

Note that the aspect implements the Ordered interface so we can set the precedence of the

aspect higher than the transaction advice (we want a fresh transaction each time we retry).

The maxRetries and order properties will both be configured by Spring. The main action

happens in the doConcurrentOperation around advice. Notice that for the moment we’re

applying the retry logic to all businessService()s. We try to proceed, and if we fail with an

PessimisticLockingFailureException we simply try again unless we have exhausted all of our

retry attempts.

The corresponding Spring configuration is:

<aop:aspectj-autoproxy/>

</bean>

To refine the aspect so that it only retries idempotent operations, we might define an Idempotent

annotation:

@Retention(RetentionPolicy.RUNTIME)

public @interface Idempotent {

// marker annotation

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 214

and use the annotation to annotate the implementation of service operations. The change to the

aspect to only retry idempotent operations simply involves refining the pointcut expression so that only

@Idempotent operations match:

@Around("com.xyz.myapp.SystemArchitecture.businessService() && " +

"@annotation(com.xyz.myapp.service.Idempotent)")

public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {

...

}

9.3 Schema-based AOP support

If you prefer an XML-based format, then Spring also offers support for defining aspects using the new

"aop" namespace tags. The exact same pointcut expressions and advice kinds are supported as when

using the @AspectJ style, hence in this section we will focus on the new syntax and refer the reader to

the discussion in the previous section (Section 9.2, “@AspectJ support”) for an understanding of writing

pointcut expressions and the binding of advice parameters.

To use the aop namespace tags described in this section, you need to import the spring-aop schema as

described in Chapter 34, XML Schema-based configuration. See the section called “the aop schema”

for how to import the tags in the aop namespace.

Within your Spring configurations, all aspect and advisor elements must be placed within an

<aop:config> element (you can have more than one <aop:config> element in an application

context configuration). An <aop:config> element can contain pointcut, advisor, and aspect elements

(note these must be declared in that order).

Warning

The <aop:config> style of configuration makes heavy use of Spring’s auto-proxying

mechanism. This can cause issues (such as advice not being woven) if you are already

using explicit auto-proxying via the use of BeanNameAutoProxyCreator or suchlike. The

recommended usage pattern is to use either just the <aop:config> style, or just the

AutoProxyCreator style.

Declaring an aspect

Using the schema support, an aspect is simply a regular Java object defined as a bean in your Spring

application context. The state and behavior is captured in the fields and methods of the object, and the

pointcut and advice information is captured in the XML.

An aspect is declared using the <aop:aspect> element, and the backing bean is referenced using the

ref attribute:

<aop:config>

<aop:aspect id="myAspect" ref="aBean">

...

</aop:aspect>

</aop:config>

...

</bean>

The bean backing the aspect (" aBean" in this case) can of course be configured and dependency

injected just like any other Spring bean.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 215

Declaring a pointcut

A named pointcut can be declared inside an <aop:config> element, enabling the pointcut definition to

be shared across several aspects and advisors.

A pointcut representing the execution of any business service in the service layer could be defined as

follows:

<aop:config>

<aop:pointcut id="businessService"

expression="execution(* com.xyz.myapp.service..(..))"/>

</aop:config>

Note that the pointcut expression itself is using the same AspectJ pointcut expression language as

described in Section 9.2, “@AspectJ support”. If you are using the schema based declaration style, you

can refer to named pointcuts defined in types (@Aspects) within the pointcut expression. Another way

of defining the above pointcut would be:

<aop:config>

<aop:pointcut id="businessService"

expression="com.xyz.myapp.SystemArchitecture.businessService()"/>

</aop:config>

Assuming you have a SystemArchitecture aspect as described in the section called “Sharing

common pointcut definitions”.

Declaring a pointcut inside an aspect is very similar to declaring a top-level pointcut:

<aop:config>

<aop:aspect id="myAspect" ref="aBean">

<aop:pointcut id="businessService"

expression="execution(* com.xyz.myapp.service..(..))"/>

...

</aop:aspect>

</aop:config>

Much the same way in an @AspectJ aspect, pointcuts declared using the schema based definition style

may collect join point context. For example, the following pointcut collects the this object as the join

point context and passes it to advice:

<aop:config>

<aop:aspect id="myAspect" ref="aBean">

<aop:pointcut id="businessService"

expression="execution(* com.xyz.myapp.service..(..)) && this(service)"/>

<aop:before pointcut-ref="businessService" method="monitor"/>

...

</aop:aspect>

</aop:config>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 216

The advice must be declared to receive the collected join point context by including parameters of the

matching names:

public void monitor(Object service) {

...

}

When combining pointcut sub-expressions, && is awkward within an XML document, and so the

keywords and, or and not can be used in place of &&, || and ! respectively. For example, the previous

pointcut may be better written as:

<aop:config>

<aop:aspect id="myAspect" ref="aBean">

<aop:pointcut id="businessService"

expression="execution(* com.xyz.myapp.service..(..)) and this(service)"/>

<aop:before pointcut-ref="businessService" method="monitor"/>

...

</aop:aspect>

</aop:config>

Note that pointcuts defined in this way are referred to by their XML id and cannot be used as named

pointcuts to form composite pointcuts. The named pointcut support in the schema based definition style

is thus more limited than that offered by the @AspectJ style.

Declaring advice

The same five advice kinds are supported as for the @AspectJ style, and they have exactly the same

semantics.

Before advice

Before advice runs before a matched method execution. It is declared inside an <aop:aspect> using

the <aop:before> element.

<aop:aspect id="beforeExample" ref="aBean">

<aop:before

pointcut-ref="dataAccessOperation"

method="doAccessCheck"/>

...

</aop:aspect>

Here dataAccessOperation is the id of a pointcut defined at the top ( <aop:config>) level. To

define the pointcut inline instead, replace the pointcut-ref attribute with a pointcut attribute:

<aop:aspect id="beforeExample" ref="aBean">

<aop:before

pointcut="execution(* com.xyz.myapp.dao..(..))"

method="doAccessCheck"/>

...

</aop:aspect>

As we noted in the discussion of the @AspectJ style, using named pointcuts can significantly improve

the readability of your code.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 217

The method attribute identifies a method ( doAccessCheck) that provides the body of the advice. This

method must be defined for the bean referenced by the aspect element containing the advice. Before a

data access operation is executed (a method execution join point matched by the pointcut expression),

the "doAccessCheck" method on the aspect bean will be invoked.

After returning advice

After returning advice runs when a matched method execution completes normally. It is declared inside

an <aop:aspect> in the same way as before advice. For example:

<aop:aspect id="afterReturningExample" ref="aBean">

<aop:after-returning

pointcut-ref="dataAccessOperation"

method="doAccessCheck"/>

...

</aop:aspect>

Just as in the @AspectJ style, it is possible to get hold of the return value within the advice body. Use

the returning attribute to specify the name of the parameter to which the return value should be passed:

<aop:aspect id="afterReturningExample" ref="aBean">

<aop:after-returning

pointcut-ref="dataAccessOperation"

returning="retVal"

method="doAccessCheck"/>

...

</aop:aspect>

The doAccessCheck method must declare a parameter named retVal. The type of this parameter

constrains matching in the same way as described for @AfterReturning. For example, the method

signature may be declared as:

public void doAccessCheck(Object retVal) {...

After throwing advice

After throwing advice executes when a matched method execution exits by throwing an exception. It is

declared inside an <aop:aspect> using the after-throwing element:

<aop:aspect id="afterThrowingExample" ref="aBean">

<aop:after-throwing

pointcut-ref="dataAccessOperation"

method="doRecoveryActions"/>

...

</aop:aspect>

Just as in the @AspectJ style, it is possible to get hold of the thrown exception within the advice body.

Use the throwing attribute to specify the name of the parameter to which the exception should be passed:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 218

<aop:aspect id="afterThrowingExample" ref="aBean">

<aop:after-throwing

pointcut-ref="dataAccessOperation"

throwing="dataAccessEx"

method="doRecoveryActions"/>

...

</aop:aspect>

The doRecoveryActions method must declare a parameter named dataAccessEx. The type of this

parameter constrains matching in the same way as described for @AfterThrowing. For example, the

method signature may be declared as:

public void doRecoveryActions(DataAccessException dataAccessEx) {...

After (finally) advice

After (finally) advice runs however a matched method execution exits. It is declared using the after

element:

<aop:aspect id="afterFinallyExample" ref="aBean">

<aop:after

pointcut-ref="dataAccessOperation"

method="doReleaseLock"/>

...

</aop:aspect>

Around advice

The final kind of advice is around advice. Around advice runs "around" a matched method execution.

It has the opportunity to do work both before and after the method executes, and to determine when,

how, and even if, the method actually gets to execute at all. Around advice is often used if you need

to share state before and after a method execution in a thread-safe manner (starting and stopping a

timer for example). Always use the least powerful form of advice that meets your requirements; don’t

use around advice if simple before advice would do.

Around advice is declared using the aop:around element. The first parameter of the advice method

must be of type ProceedingJoinPoint. Within the body of the advice, calling proceed() on the

ProceedingJoinPoint causes the underlying method to execute. The proceed method may also

be calling passing in an Object[] - the values in the array will be used as the arguments to the method

execution when it proceeds. See the section called “Around advice” for notes on calling proceed with

an Object[].

<aop:aspect id="aroundExample" ref="aBean">

<aop:around

pointcut-ref="businessService"

method="doBasicProfiling"/>

...

</aop:aspect>

The implementation of the doBasicProfiling advice would be exactly the same as in the @AspectJ

example (minus the annotation of course):

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 219

public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable {

// start stopwatch

Object retVal = pjp.proceed();

// stop stopwatch

return retVal;

}

Advice parameters

The schema based declaration style supports fully typed advice in the same way as described for the

@AspectJ support - by matching pointcut parameters by name against advice method parameters. See

the section called “Advice parameters” for details. If you wish to explicitly specify argument names for

the advice methods (not relying on the detection strategies previously described) then this is done using

the arg-names attribute of the advice element, which is treated in the same manner to the "argNames"

attribute in an advice annotation as described in the section called “Determining argument names”. For

example:

<aop:before

pointcut="com.xyz.lib.Pointcuts.anyPublicMethod() and @annotation(auditable)"

method="audit"

arg-names="auditable"/>

The arg-names attribute accepts a comma-delimited list of parameter names.

Find below a slightly more involved example of the XSD-based approach that illustrates some around

advice used in conjunction with a number of strongly typed parameters.

package x.y.service;

public interface FooService {

Foo getFoo(String fooName, int age);

}

public class DefaultFooService implements FooService {

public Foo getFoo(String name, int age) {

return new Foo(name, age);

}

Next up is the aspect. Notice the fact that the profile(..) method accepts a number of strongly-

typed parameters, the first of which happens to be the join point used to proceed with the method call:

the presence of this parameter is an indication that the profile(..) is to be used as around advice:

package x.y;

import org.aspectj.lang.ProceedingJoinPoint;

import org.springframework.util.StopWatch;

public class SimpleProfiler {

public Object profile(ProceedingJoinPoint call, String name, int age) throws Throwable {

StopWatch clock = new StopWatch("Profiling for " + name + " and " + age + "");

try {

clock.start(call.toShortString());

return call.proceed();

} finally {

clock.stop();

System.out.println(clock.prettyPrint());

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 220

Finally, here is the XML configuration that is required to effect the execution of the above advice for

a particular join point:

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xsi:schemaLocation="

http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-

beans.xsd

http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-

aop.xsd">

<aop:config>

<aop:aspect ref="profiler">

<aop:pointcut id="theExecutionOfSomeFooServiceMethod"

expression="execution(* x.y.service.FooService.getFoo(String,int))

and args(name, age)"/>

<aop:around pointcut-ref="theExecutionOfSomeFooServiceMethod"

method="profile"/>

</aop:aspect>

</aop:config>

</beans>

If we had the following driver script, we would get output something like this on standard output:

import org.springframework.beans.factory.BeanFactory;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import x.y.service.FooService;

public final class Boot {

public static void main(final String[] args) throws Exception {

BeanFactory ctx = new ClassPathXmlApplicationContext("x/y/plain.xml");

FooService foo = (FooService) ctx.getBean("fooService");

foo.getFoo("Pengo", 12);

}

StopWatch Profiling for 'Pengo and 12': running time (millis) = 0

-----------------------------------------

ms % Task name

-----------------------------------------

00000 ? execution(getFoo)

Advice ordering

When multiple advice needs to execute at the same join point (executing method) the ordering rules are

as described in the section called “Advice ordering”. The precedence between aspects is determined

by either adding the Order annotation to the bean backing the aspect or by having the bean implement

the Ordered interface.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 221

Introductions

Introductions (known as inter-type declarations in AspectJ) enable an aspect to declare that advised

objects implement a given interface, and to provide an implementation of that interface on behalf of

those objects.

An introduction is made using the aop:declare-parents element inside an aop:aspect This

element is used to declare that matching types have a new parent (hence the name). For example, given

an interface UsageTracked, and an implementation of that interface DefaultUsageTracked, the

following aspect declares that all implementors of service interfaces also implement the UsageTracked

interface. (In order to expose statistics via JMX for example.)

<aop:aspect id="usageTrackerAspect" ref="usageTracking">

<aop:declare-parents

types-matching="com.xzy.myapp.service.*+"

implement-interface="com.xyz.myapp.service.tracking.UsageTracked"

default-impl="com.xyz.myapp.service.tracking.DefaultUsageTracked"/>

<aop:before

pointcut="com.xyz.myapp.SystemArchitecture.businessService()

and this(usageTracked)"

method="recordUsage"/>

</aop:aspect>

The class backing the usageTracking bean would contain the method:

public void recordUsage(UsageTracked usageTracked) {

usageTracked.incrementUseCount();

}

The interface to be implemented is determined by implement-interface attribute. The value of the

types-matching attribute is an AspectJ type pattern :- any bean of a matching type will implement the

UsageTracked interface. Note that in the before advice of the above example, service beans can be

directly used as implementations of the UsageTracked interface. If accessing a bean programmatically

you would write the following:

UsageTracked usageTracked = (UsageTracked) context.getBean("myService");

Aspect instantiation models

The only supported instantiation model for schema-defined aspects is the singleton model. Other

instantiation models may be supported in future releases.

Advisors

The concept of "advisors" is brought forward from the AOP support defined in Spring 1.2 and does not

have a direct equivalent in AspectJ. An advisor is like a small self-contained aspect that has a single

piece of advice. The advice itself is represented by a bean, and must implement one of the advice

interfaces described in the section called “Advice types in Spring”. Advisors can take advantage of

AspectJ pointcut expressions though.

Spring supports the advisor concept with the <aop:advisor> element. You will most commonly see

it used in conjunction with transactional advice, which also has its own namespace support in Spring.

Here’s how it looks:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 222

<aop:config>

<aop:pointcut id="businessService"

expression="execution(* com.xyz.myapp.service..(..))"/>

<aop:advisor

pointcut-ref="businessService"

advice-ref="tx-advice"/>

</aop:config>

<tx:advice id="tx-advice">

<tx:attributes>

<tx:method name="*" propagation="REQUIRED"/>

</tx:attributes>

</tx:advice>

As well as the pointcut-ref attribute used in the above example, you can also use the pointcut

attribute to define a pointcut expression inline.

To define the precedence of an advisor so that the advice can participate in ordering, use the order

attribute to define the Ordered value of the advisor.

Example

Let’s see how the concurrent locking failure retry example from the section called “Example” looks when

rewritten using the schema support.

The execution of business services can sometimes fail due to concurrency issues (for example, deadlock

loser). If the operation is retried, it is quite likely it will succeed next time round. For business services

where it is appropriate to retry in such conditions (idempotent operations that don’t need to go back to

the user for conflict resolution), we’d like to transparently retry the operation to avoid the client seeing

a PessimisticLockingFailureException. This is a requirement that clearly cuts across multiple

services in the service layer, and hence is ideal for implementing via an aspect.

Because we want to retry the operation, we’ll need to use around advice so that we can call proceed

multiple times. Here’s how the basic aspect implementation looks (it’s just a regular Java class using

the schema support):

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 223

public class ConcurrentOperationExecutor implements Ordered {

private static final int DEFAULT_MAX_RETRIES = 2;

private int maxRetries = DEFAULT_MAX_RETRIES;

private int order = 1;

public void setMaxRetries(int maxRetries) {

this.maxRetries = maxRetries;

}

public int getOrder() {

return this.order;

}

public void setOrder(int order) {

this.order = order;

}

public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {

int numAttempts = 0;

PessimisticLockingFailureException lockFailureException;

do {

numAttempts++;

try {

return pjp.proceed();

}

catch(PessimisticLockingFailureException ex) {

lockFailureException = ex;

}

} while(numAttempts <= this.maxRetries);

throw lockFailureException;

}

Note that the aspect implements the Ordered interface so we can set the precedence of the

aspect higher than the transaction advice (we want a fresh transaction each time we retry). The

maxRetries and order properties will both be configured by Spring. The main action happens

in the doConcurrentOperation around advice method. We try to proceed, and if we fail with a

PessimisticLockingFailureException we simply try again unless we have exhausted all of our

retry attempts.

Note

This class is identical to the one used in the @AspectJ example, but with the annotations removed.

The corresponding Spring configuration is:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 224

<aop:config>

<aop:aspect id="concurrentOperationRetry" ref="concurrentOperationExecutor">

<aop:pointcut id="idempotentOperation"

expression="execution(* com.xyz.myapp.service..(..))"/>

<aop:around

pointcut-ref="idempotentOperation"

method="doConcurrentOperation"/>

</aop:aspect>

</aop:config>

<bean id="concurrentOperationExecutor"

class="com.xyz.myapp.service.impl.ConcurrentOperationExecutor">

</bean>

Notice that for the time being we assume that all business services are idempotent. If this is not the

case we can refine the aspect so that it only retries genuinely idempotent operations, by introducing

an Idempotent annotation:

@Retention(RetentionPolicy.RUNTIME)

public @interface Idempotent {

// marker annotation

}

and using the annotation to annotate the implementation of service operations. The change to the

aspect to retry only idempotent operations simply involves refining the pointcut expression so that only

@Idempotent operations match:

<aop:pointcut id="idempotentOperation"

expression="execution(* com.xyz.myapp.service..(..)) and

@annotation(com.xyz.myapp.service.Idempotent)"/>

9.4 Choosing which AOP declaration style to use

Once you have decided that an aspect is the best approach for implementing a given requirement, how

do you decide between using Spring AOP or AspectJ, and between the Aspect language (code) style,

@AspectJ annotation style, or the Spring XML style? These decisions are influenced by a number of

factors including application requirements, development tools, and team familiarity with AOP.

Spring AOP or full AspectJ?

Use the simplest thing that can work. Spring AOP is simpler than using full AspectJ as there is no

requirement to introduce the AspectJ compiler / weaver into your development and build processes.

If you only need to advise the execution of operations on Spring beans, then Spring AOP is the right

choice. If you need to advise objects not managed by the Spring container (such as domain objects

typically), then you will need to use AspectJ. You will also need to use AspectJ if you wish to advise join

points other than simple method executions (for example, field get or set join points, and so on).

When using AspectJ, you have the choice of the AspectJ language syntax (also known as the "code

style") or the @AspectJ annotation style. Clearly, if you are not using Java 5+ then the choice has been

made for you… use the code style. If aspects play a large role in your design, and you are able to use

the AspectJ Development Tools (AJDT) plugin for Eclipse, then the AspectJ language syntax is the

preferred option: it is cleaner and simpler because the language was purposefully designed for writing

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 225

aspects. If you are not using Eclipse, or have only a few aspects that do not play a major role in your

application, then you may want to consider using the @AspectJ style and sticking with a regular Java

compilation in your IDE, and adding an aspect weaving phase to your build script.

@AspectJ or XML for Spring AOP?

If you have chosen to use Spring AOP, then you have a choice of @AspectJ or XML style. There are

various tradeoffs to consider.

The XML style will be most familiar to existing Spring users and it is backed by genuine POJOs. When

using AOP as a tool to configure enterprise services then XML can be a good choice (a good test

is whether you consider the pointcut expression to be a part of your configuration you might want to

change independently). With the XML style arguably it is clearer from your configuration what aspects

are present in the system.

The XML style has two disadvantages. Firstly it does not fully encapsulate the implementation of the

requirement it addresses in a single place. The DRY principle says that there should be a single,

unambiguous, authoritative representation of any piece of knowledge within a system. When using the

XML style, the knowledge of how a requirement is implemented is split across the declaration of the

backing bean class, and the XML in the configuration file. When using the @AspectJ style there is a

single module - the aspect - in which this information is encapsulated. Secondly, the XML style is slightly

more limited in what it can express than the @AspectJ style: only the "singleton" aspect instantiation

model is supported, and it is not possible to combine named pointcuts declared in XML. For example,

in the @AspectJ style you can write something like:

@Pointcut(execution(* get*()))

public void propertyAccess() {}

@Pointcut(execution(org.xyz.Account+ *(..))

public void operationReturningAnAccount() {}

@Pointcut(propertyAccess() && operationReturningAnAccount())

public void accountPropertyAccess() {}

In the XML style I can declare the first two pointcuts:

<aop:pointcut id="propertyAccess"

expression="execution(* get*())"/>

<aop:pointcut id="operationReturningAnAccount"

expression="execution(org.xyz.Account+ *(..))"/>

The downside of the XML approach is that you cannot define the accountPropertyAccess pointcut

by combining these definitions.

The @AspectJ style supports additional instantiation models, and richer pointcut composition. It has the

advantage of keeping the aspect as a modular unit. It also has the advantage the @AspectJ aspects

can be understood (and thus consumed) both by Spring AOP and by AspectJ - so if you later decide

you need the capabilities of AspectJ to implement additional requirements then it is very easy to migrate

to an AspectJ-based approach. On balance the Spring team prefer the @AspectJ style whenever you

have aspects that do more than simple "configuration" of enterprise services.

9.5 Mixing aspect types

It is perfectly possible to mix @AspectJ style aspects using the autoproxying support, schema-defined

<aop:aspect> aspects, <aop:advisor> declared advisors and even proxies and interceptors

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 226

defined using the Spring 1.2 style in the same configuration. All of these are implemented using the

same underlying support mechanism and will co-exist without any difficulty.

9.6 Proxying mechanisms

Spring AOP uses either JDK dynamic proxies or CGLIB to create the proxy for a given target object.

(JDK dynamic proxies are preferred whenever you have a choice).

If the target object to be proxied implements at least one interface then a JDK dynamic proxy will be

used. All of the interfaces implemented by the target type will be proxied. If the target object does not

implement any interfaces then a CGLIB proxy will be created.

If you want to force the use of CGLIB proxying (for example, to proxy every method defined for the

target object, not just those implemented by its interfaces) you can do so. However, there are some

issues to consider:

•final methods cannot be advised, as they cannot be overridden.

• As of Spring 3.2, it is no longer necessary to add CGLIB to your project classpath, as CGLIB classes

are repackaged under org.springframework and included directly in the spring-core JAR. This means

that CGLIB-based proxy support just works in the same way that JDK dynamic proxies always have.

• The constructor of your proxied object will be called twice. This is a natural consequence of the CGLIB

proxy model whereby a subclass is generated for each proxied object. For each proxied instance, two

objects are created: the actual proxied object and an instance of the subclass that implements the

advice. This behavior is not exhibited when using JDK proxies. Usually, calling the constructor of the

proxied type twice, is not an issue, as there are usually only assignments taking place and no real

logic is implemented in the constructor.

To force the use of CGLIB proxies set the value of the proxy-target-class attribute of the

<aop:config> element to true:

<aop:config proxy-target-class="true">

</aop:config>

To force CGLIB proxying when using the @AspectJ autoproxy support, set the 'proxy-target-

class' attribute of the <aop:aspectj-autoproxy> element to true:

<aop:aspectj-autoproxy proxy-target-class="true"/>

Note

Multiple <aop:config/> sections are collapsed into a single unified auto-proxy creator

at runtime, which applies the strongest proxy settings that any of the <aop:config/>

sections (typically from different XML bean definition files) specified. This also applies to the

<tx:annotation-driven/> and <aop:aspectj-autoproxy/> elements.

To be clear: using proxy-target-class="true" on <tx:annotation-driven/>,

<aop:aspectj-autoproxy/> or <aop:config/> elements will force the use of CGLIB

proxies for all three of them.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 227

Understanding AOP proxies

Spring AOP is proxy-based. It is vitally important that you grasp the semantics of what that last statement

actually means before you write your own aspects or use any of the Spring AOP-based aspects supplied

with the Spring Framework.

Consider first the scenario where you have a plain-vanilla, un-proxied, nothing-special-about-it, straight

object reference, as illustrated by the following code snippet.

public class SimplePojo implements Pojo {

public void foo() {

// this next method invocation is a direct call on the this reference

this.bar();

}

public void bar() {

// some logic...

}

If you invoke a method on an object reference, the method is invoked directly on that object reference,

as can be seen below.

Figure 9.1.

public class Main {

public static void main(String[] args) {

Pojo pojo = new SimplePojo();

// this is a direct method call on the pojo reference

pojo.foo();

}

Things change slightly when the reference that client code has is a proxy. Consider the following diagram

and code snippet.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 228

Figure 9.2.

public class Main {

public static void main(String[] args) {

ProxyFactory factory = new ProxyFactory(new SimplePojo());

factory.addInterface(Pojo.class);

factory.addAdvice(new RetryAdvice());

Pojo pojo = (Pojo) factory.getProxy();

// this is a method call on the proxy!

pojo.foo();

}

The key thing to understand here is that the client code inside the main(..) of the Main class

has a reference to the proxy. This means that method calls on that object reference will be calls on

the proxy, and as such the proxy will be able to delegate to all of the interceptors (advice) that are

relevant to that particular method call. However, once the call has finally reached the target object, the

SimplePojo reference in this case, any method calls that it may make on itself, such as this.bar() or

this.foo(), are going to be invoked against the this reference, and not the proxy. This has important

implications. It means that self-invocation is not going to result in the advice associated with a method

invocation getting a chance to execute.

Okay, so what is to be done about this? The best approach (the term best is used loosely here) is to

refactor your code such that the self-invocation does not happen. For sure, this does entail some work

on your part, but it is the best, least-invasive approach. The next approach is absolutely horrendous,

and I am almost reticent to point it out precisely because it is so horrendous. You can (choke!) totally

tie the logic within your class to Spring AOP by doing this:

public class SimplePojo implements Pojo {

public void foo() {

// this works, but... gah!

((Pojo) AopContext.currentProxy()).bar();

}

public void bar() {

// some logic...

}

This totally couples your code to Spring AOP, and it makes the class itself aware of the fact that it is being

used in an AOP context, which flies in the face of AOP. It also requires some additional configuration

when the proxy is being created:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 229

public class Main {

public static void main(String[] args) {

ProxyFactory factory = new ProxyFactory(new SimplePojo());

factory.adddInterface(Pojo.class);

factory.addAdvice(new RetryAdvice());

factory.setExposeProxy(true);

Pojo pojo = (Pojo) factory.getProxy();

// this is a method call on the proxy!

pojo.foo();

}

Finally, it must be noted that AspectJ does not have this self-invocation issue because it is not a proxy-

based AOP framework.

9.7 Programmatic creation of @AspectJ Proxies

In addition to declaring aspects in your configuration using either <aop:config> or <aop:aspectj-

autoproxy>, it is also possible programmatically to create proxies that advise target objects. For the full

details of Spring’s AOP API, see the next chapter. Here we want to focus on the ability to automatically

create proxies using @AspectJ aspects.

The class org.springframework.aop.aspectj.annotation.AspectJProxyFactory can be

used to create a proxy for a target object that is advised by one or more @AspectJ aspects. Basic usage

for this class is very simple, as illustrated below. See the javadocs for full information.

// create a factory that can generate a proxy for the given target object

AspectJProxyFactory factory = new AspectJProxyFactory(targetObject);

// add an aspect, the class must be an @AspectJ aspect

// you can call this as many times as you need with different aspects

factory.addAspect(SecurityManager.class);

// you can also add existing aspect instances, the type of the object supplied must be an @AspectJ

aspect

factory.addAspect(usageTracker);

// now get the proxy object...

MyInterfaceType proxy = factory.getProxy();

9.8 Using AspectJ with Spring applications

Everything we’ve covered so far in this chapter is pure Spring AOP. In this section, we’re going to look

at how you can use the AspectJ compiler/weaver instead of, or in addition to, Spring AOP if your needs

go beyond the facilities offered by Spring AOP alone.

Spring ships with a small AspectJ aspect library, which is available standalone in your distribution as

spring-aspects.jar; you’ll need to add this to your classpath in order to use the aspects in it. the

section called “Using AspectJ to dependency inject domain objects with Spring” and the section called

“Other Spring aspects for AspectJ” discuss the content of this library and how you can use it. the section

called “Configuring AspectJ aspects using Spring IoC” discusses how to dependency inject AspectJ

aspects that are woven using the AspectJ compiler. Finally, the section called “Load-time weaving with

AspectJ in the Spring Framework” provides an introduction to load-time weaving for Spring applications

using AspectJ.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 230

Using AspectJ to dependency inject domain objects with Spring

The Spring container instantiates and configures beans defined in your application context. It is also

possible to ask a bean factory to configure a pre-existing object given the name of a bean definition

containing the configuration to be applied. The spring-aspects.jar contains an annotation-driven

aspect that exploits this capability to allow dependency injection of any object. The support is intended

to be used for objects created outside of the control of any container. Domain objects often fall into this

category because they are often created programmatically using the new operator, or by an ORM tool

as a result of a database query.

The @Configurable annotation marks a class as eligible for Spring-driven configuration. In the

simplest case it can be used just as a marker annotation:

package com.xyz.myapp.domain;

import org.springframework.beans.factory.annotation.Configurable;

@Configurable

public class Account {

// ...

}

When used as a marker interface in this way, Spring will configure new instances of the annotated type

( Account in this case) using a bean definition (typically prototype-scoped) with the same name as the

fully-qualified type name ( com.xyz.myapp.domain.Account). Since the default name for a bean

is the fully-qualified name of its type, a convenient way to declare the prototype definition is simply to

omit the id attribute:

</bean>

If you want to explicitly specify the name of the prototype bean definition to use, you can do so directly

in the annotation:

package com.xyz.myapp.domain;

import org.springframework.beans.factory.annotation.Configurable;

@Configurable("account")

public class Account {

// ...

}

Spring will now look for a bean definition named " account" and use that as the definition to configure

new Account instances.

You can also use autowiring to avoid having to specify a dedicated bean definition

at all. To have Spring apply autowiring use the autowire property of the

@Configurable annotation: specify either @Configurable(autowire=Autowire.BY_TYPE) or

@Configurable(autowire=Autowire.BY_NAME for autowiring by type or by name respectively. As

an alternative, as of Spring 2.5 it is preferable to specify explicit, annotation-driven dependency injection

for your @Configurable beans by using @Autowired or @Inject at the field or method level (see

Section 5.9, “Annotation-based container configuration” for further details).

Finally you can enable Spring dependency checking for the object references in the

newly created and configured object by using the dependencyCheck attribute (for example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 231

@Configurable(autowire=Autowire.BY_NAME,dependencyCheck=true)). If this attribute is

set to true, then Spring will validate after configuration that all properties (which are not primitives or

collections) have been set.

Using the annotation on its own does nothing of course. It is the

AnnotationBeanConfigurerAspect in spring-aspects.jar that acts on the presence of the

annotation. In essence the aspect says "after returning from the initialization of a new object of a type

annotated with @Configurable, configure the newly created object using Spring in accordance with

the properties of the annotation". In this context, initialization refers to newly instantiated objects (e.g.,

objects instantiated with the new operator) as well as to Serializable objects that are undergoing

deserialization (e.g., via readResolve()).

Note

One of the key phrases in the above paragraph is in essence. For most cases, the exact

semantics of after returning from the initialization of a new object will be fine… in this context, after

initialization means that the dependencies will be injected after the object has been constructed

- this means that the dependencies will not be available for use in the constructor bodies of the

class. If you want the dependencies to be injected before the constructor bodies execute, and

thus be available for use in the body of the constructors, then you need to define this on the

@Configurable declaration like so:

@Configurable(preConstruction=true)

You can find out more information about the language semantics of the various pointcut types in

AspectJ in this appendix of the AspectJ Programming Guide.

For this to work the annotated types must be woven with the AspectJ weaver - you can either use a build-

time Ant or Maven task to do this (see for example the AspectJ Development Environment Guide) or

load-time weaving (see the section called “Load-time weaving with AspectJ in the Spring Framework”).

The AnnotationBeanConfigurerAspect itself needs configuring by Spring (in order to obtain a

reference to the bean factory that is to be used to configure new objects). If you are using Java based

configuration simply add @EnableSpringConfigured to any @Configuration class.

@Configuration

@EnableSpringConfigured

public class AppConfig {

}

If you prefer XML based configuration, the Spring context namespace defines a convenient

context:spring-configured element:

<context:spring-configured/>

Instances of @Configurable objects created before the aspect has been configured will result in a

message being issued to the debug log and no configuration of the object taking place. An example

might be a bean in the Spring configuration that creates domain objects when it is initialized by Spring.

In this case you can use the "depends-on" bean attribute to manually specify that the bean depends

on the configuration aspect.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 232

<bean id="myService"

class="com.xzy.myapp.service.MyService"

depends-on="org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect">

</bean>

Note

Do not activate @Configurable processing through the bean configurer aspect unless you

really mean to rely on its semantics at runtime. In particular, make sure that you do not

use @Configurable on bean classes which are registered as regular Spring beans with the

container: You would get double initialization otherwise, once through the container and once

through the aspect.

Unit testing @Configurable objects

One of the goals of the @Configurable support is to enable independent unit testing of domain objects

without the difficulties associated with hard-coded lookups. If @Configurable types have not been

woven by AspectJ then the annotation has no affect during unit testing, and you can simply set mock

or stub property references in the object under test and proceed as normal. If @Configurable types

have been woven by AspectJ then you can still unit test outside of the container as normal, but you will

see a warning message each time that you construct an @Configurable object indicating that it has

not been configured by Spring.

Working with multiple application contexts

The AnnotationBeanConfigurerAspect used to implement the @Configurable support is an

AspectJ singleton aspect. The scope of a singleton aspect is the same as the scope of static

members, that is to say there is one aspect instance per classloader that defines the type. This

means that if you define multiple application contexts within the same classloader hierarchy you need

to consider where to define the @EnableSpringConfigured bean and where to place spring-

aspects.jar on the classpath.

Consider a typical Spring web-app configuration with a shared parent application context defining

common business services and everything needed to support them, and one child application context

per servlet containing definitions particular to that servlet. All of these contexts will co-exist within

the same classloader hierarchy, and so the AnnotationBeanConfigurerAspect can only hold a

reference to one of them. In this case we recommend defining the @EnableSpringConfigured bean

in the shared (parent) application context: this defines the services that you are likely to want to inject

into domain objects. A consequence is that you cannot configure domain objects with references to

beans defined in the child (servlet-specific) contexts using the @Configurable mechanism (probably not

something you want to do anyway!).

When deploying multiple web-apps within the same container, ensure that each web-application loads

the types in spring-aspects.jar using its own classloader (for example, by placing spring-

aspects.jar in 'WEB-INF/lib'). If spring-aspects.jar is only added to the container wide

classpath (and hence loaded by the shared parent classloader), all web applications will share the same

aspect instance which is probably not what you want.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 233

Other Spring aspects for AspectJ

In addition to the @Configurable aspect, spring-aspects.jar contains an AspectJ aspect

that can be used to drive Spring’s transaction management for types and methods annotated with

the @Transactional annotation. This is primarily intended for users who want to use the Spring

Framework’s transaction support outside of the Spring container.

The aspect that interprets @Transactional annotations is the AnnotationTransactionAspect.

When using this aspect, you must annotate the implementation class (and/or methods within that class),

not the interface (if any) that the class implements. AspectJ follows Java’s rule that annotations on

interfaces are not inherited.

A @Transactional annotation on a class specifies the default transaction semantics for the execution

of any public operation in the class.

A @Transactional annotation on a method within the class overrides the default transaction

semantics given by the class annotation (if present). Methods with public, protected, and default

visibility may all be annotated. Annotating protected and default visibility methods directly is the only

way to get transaction demarcation for the execution of such methods.

For AspectJ programmers that want to use the Spring configuration and transaction management

support but don’t want to (or cannot) use annotations, spring-aspects.jar also contains

abstract aspects you can extend to provide your own pointcut definitions. See the sources for

the AbstractBeanConfigurerAspect and AbstractTransactionAspect aspects for more

information. As an example, the following excerpt shows how you could write an aspect to configure

all instances of objects defined in the domain model using prototype bean definitions that match the

fully-qualified class names:

public aspect DomainObjectConfiguration extends AbstractBeanConfigurerAspect {

public DomainObjectConfiguration() {

setBeanWiringInfoResolver(new ClassNameBeanWiringInfoResolver());

}

// the creation of a new bean (any object in the domain model)

protected pointcut beanCreation(Object beanInstance) :

initialization(new(..)) &&

SystemArchitecture.inDomainModel() &&

this(beanInstance);

}

Configuring AspectJ aspects using Spring IoC

When using AspectJ aspects with Spring applications, it is natural to both want and expect to be able to

configure such aspects using Spring. The AspectJ runtime itself is responsible for aspect creation, and

the means of configuring the AspectJ created aspects via Spring depends on the AspectJ instantiation

model (the per-xxx clause) used by the aspect.

The majority of AspectJ aspects are singleton aspects. Configuration of these aspects is very easy:

simply create a bean definition referencing the aspect type as normal, and include the bean attribute

'factory-method="aspectOf"'. This ensures that Spring obtains the aspect instance by asking

AspectJ for it rather than trying to create an instance itself. For example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 234

<bean id="profiler" class="com.xyz.profiler.Profiler"

factory-method="aspectOf">

</bean>

Non-singleton aspects are harder to configure: however it is possible to do so by creating prototype

bean definitions and using the @Configurable support from spring-aspects.jar to configure the

aspect instances once they have bean created by the AspectJ runtime.

If you have some @AspectJ aspects that you want to weave with AspectJ (for example, using load-time

weaving for domain model types) and other @AspectJ aspects that you want to use with Spring AOP,

and these aspects are all configured using Spring, then you will need to tell the Spring AOP @AspectJ

autoproxying support which exact subset of the @AspectJ aspects defined in the configuration should

be used for autoproxying. You can do this by using one or more <include/> elements inside the

<aop:aspectj-autoproxy/> declaration. Each <include/> element specifies a name pattern, and

only beans with names matched by at least one of the patterns will be used for Spring AOP autoproxy

configuration:

<aop:aspectj-autoproxy>

<aop:include name="thisBean"/>

<aop:include name="thatBean"/>

</aop:aspectj-autoproxy>

Note

Do not be misled by the name of the <aop:aspectj-autoproxy/> element: using it will result

in the creation of Spring AOP proxies. The @AspectJ style of aspect declaration is just being used

here, but the AspectJ runtime is not involved.

Load-time weaving with AspectJ in the Spring Framework

Load-time weaving (LTW) refers to the process of weaving AspectJ aspects into an application’s class

files as they are being loaded into the Java virtual machine (JVM). The focus of this section is on

configuring and using LTW in the specific context of the Spring Framework: this section is not an

introduction to LTW though. For full details on the specifics of LTW and configuring LTW with just AspectJ

(with Spring not being involved at all), see the LTW section of the AspectJ Development Environment

Guide.

The value-add that the Spring Framework brings to AspectJ LTW is in enabling much finer-grained

control over the weaving process. Vanilla AspectJ LTW is effected using a Java (5+) agent, which is

switched on by specifying a VM argument when starting up a JVM. It is thus a JVM-wide setting, which

may be fine in some situations, but often is a little too coarse. Spring-enabled LTW enables you to

switch on LTW on a per-ClassLoader basis, which obviously is more fine-grained and which can make

more sense in a single-JVM-multiple-application environment (such as is found in a typical application

server environment).

Further, in certain environments, this support enables load-time weaving without making any

modifications to the application server’s launch script that will be needed to add -javaagent:path/

to/aspectjweaver.jar or (as we describe later in this section) -javaagent:path/to/

org.springframework.instrument-{version}.jar (previously named spring-agent.jar).

Developers simply modify one or more files that form the application context to enable load-time weaving

instead of relying on administrators who typically are in charge of the deployment configuration such

as the launch script.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 235

Now that the sales pitch is over, let us first walk through a quick example of AspectJ LTW using Spring,

followed by detailed specifics about elements introduced in the following example. For a complete

example, please see the Petclinic sample application.

A first example

Let us assume that you are an application developer who has been tasked with diagnosing the cause of

some performance problems in a system. Rather than break out a profiling tool, what we are going to do

is switch on a simple profiling aspect that will enable us to very quickly get some performance metrics,

so that we can then apply a finer-grained profiling tool to that specific area immediately afterwards.

Note

The example presented here uses XML style configuration, it is also possible to configure and

use @AspectJ with Java Configuration. Specifically the @EnableLoadTimeWeaving annotation

can be used as an alternative to <context:load-time-weaver/> (see below for details).

Here is the profiling aspect. Nothing too fancy, just a quick-and-dirty time-based profiler, using the

@AspectJ-style of aspect declaration.

package foo;

import org.aspectj.lang.ProceedingJoinPoint;

import org.aspectj.lang.annotation.Aspect;

import org.aspectj.lang.annotation.Around;

import org.aspectj.lang.annotation.Pointcut;

import org.springframework.util.StopWatch;

import org.springframework.core.annotation.Order;

@Aspect

public class ProfilingAspect {

@Around("methodsToBeProfiled()")

public Object profile(ProceedingJoinPoint pjp) throws Throwable {

StopWatch sw = new StopWatch(getClass().getSimpleName());

try {

sw.start(pjp.getSignature().getName());

return pjp.proceed();

} finally {

sw.stop();

System.out.println(sw.prettyPrint());

}

@Pointcut("execution(public * foo...(..))")

public void methodsToBeProfiled(){}

}

We will also need to create an META-INF/aop.xml file, to inform the AspectJ weaver that we want to

weave our ProfilingAspect into our classes. This file convention, namely the presence of a file (or

files) on the Java classpath called META-INF/aop.xml is standard AspectJ.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 236

<!DOCTYPE aspectj PUBLIC "-//AspectJ//DTD//EN" "http://www.eclipse.org/aspectj/dtd/aspectj.dtd">

</weaver>

</aspects>

</aspectj>

Now to the Spring-specific portion of the configuration. We need to configure a LoadTimeWeaver

(all explained later, just take it on trust for now). This load-time weaver is the essential component

responsible for weaving the aspect configuration in one or more META-INF/aop.xml files into the

classes in your application. The good thing is that it does not require a lot of configuration, as can be

seen below (there are some more options that you can specify, but these are detailed later).

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<bean id="entitlementCalculationService"

class="foo.StubEntitlementCalculationService"/>

<context:load-time-weaver/>

</beans>

Now that all the required artifacts are in place - the aspect, the META-INF/aop.xml file, and the Spring

configuration -, let us create a simple driver class with a main(..) method to demonstrate the LTW

in action.

package foo;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public final class Main {

public static void main(String[] args) {

ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml", Main.class);

EntitlementCalculationService entitlementCalculationService

= (EntitlementCalculationService) ctx.getBean("entitlementCalculationService");

// the profiling aspect is woven around this method execution

entitlementCalculationService.calculateEntitlement();

}

There is one last thing to do. The introduction to this section did say that one could switch on LTW

selectively on a per- ClassLoader basis with Spring, and this is true. However, just for this example,

we are going to use a Java agent (supplied with Spring) to switch on the LTW. This is the command

line we will use to run the above Main class:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 237

java -javaagent:C:/projects/foo/lib/global/spring-instrument.jar foo.Main

The -javaagent is a flag for specifying and enabling agents to instrument programs running on the

JVM. The Spring Framework ships with such an agent, the InstrumentationSavingAgent, which

is packaged in the spring-instrument.jar that was supplied as the value of the -javaagent

argument in the above example.

The output from the execution of the Main program will look something like that below. (I have introduced

a Thread.sleep(..) statement into the calculateEntitlement() implementation so that the

profiler actually captures something other than 0 milliseconds - the 01234 milliseconds is not an

overhead introduced by the AOP :) )

Calculating entitlement

StopWatch ProfilingAspect: running time (millis) = 1234

------ ----- ----------------------------

ms % Task name

------ ----- ----------------------------

01234 100% calculateEntitlement

Since this LTW is effected using full-blown AspectJ, we are not just limited to advising Spring beans;

the following slight variation on the Main program will yield the same result.

package foo;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public final class Main {

public static void main(String[] args) {

new ClassPathXmlApplicationContext("beans.xml", Main.class);

EntitlementCalculationService entitlementCalculationService =

new StubEntitlementCalculationService();

// the profiling aspect will be woven around this method execution

entitlementCalculationService.calculateEntitlement();

}

Notice how in the above program we are simply bootstrapping the Spring container, and then creating a

new instance of the StubEntitlementCalculationService totally outside the context of Spring…

the profiling advice still gets woven in.

The example admittedly is simplistic… however the basics of the LTW support in Spring have all been

introduced in the above example, and the rest of this section will explain the why behind each bit of

configuration and usage in detail.

Note

The ProfilingAspect used in this example may be basic, but it is quite useful. It is a nice

example of a development-time aspect that developers can use during development (of course),

and then quite easily exclude from builds of the application being deployed into UAT or production.

Aspects

The aspects that you use in LTW have to be AspectJ aspects. They can be written in either the AspectJ

language itself or you can write your aspects in the @AspectJ-style. It means that your aspects are

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 238

then both valid AspectJ and Spring AOP aspects. Furthermore, the compiled aspect classes need to

be available on the classpath.

META-INF/aop.xml

The AspectJ LTW infrastructure is configured using one or more META-INF/aop.xml files, that are on

the Java classpath (either directly, or more typically in jar files).

The structure and contents of this file is detailed in the main AspectJ reference documentation, and the

interested reader is referred to that resource. (I appreciate that this section is brief, but the aop.xml file

is 100% AspectJ - there is no Spring-specific information or semantics that apply to it, and so there is no

extra value that I can contribute either as a result), so rather than rehash the quite satisfactory section

that the AspectJ developers wrote, I am just directing you there.)

Required libraries (JARS)

At a minimum you will need the following libraries to use the Spring Framework’s support for AspectJ

LTW:

•spring-aop.jar (version 2.5 or later, plus all mandatory dependencies)

•aspectjweaver.jar (version 1.6.8 or later)

If you are using the Spring-provided agent to enable instrumentation, you will also need:

•spring-instrument.jar

Spring configuration

The key component in Spring’s LTW support is the LoadTimeWeaver interface (in

the org.springframework.instrument.classloading package), and the numerous

implementations of it that ship with the Spring distribution. A LoadTimeWeaver is responsible for adding

one or more java.lang.instrument.ClassFileTransformers to a ClassLoader at runtime,

which opens the door to all manner of interesting applications, one of which happens to be the LTW

of aspects.

Tip

If you are unfamiliar with the idea of runtime class file transformation, you are encouraged to read

the javadoc API documentation for the java.lang.instrument package before continuing.

This is not a huge chore because there is - rather annoyingly - precious little documentation

there… the key interfaces and classes will at least be laid out in front of you for reference as you

read through this section.

Configuring a LoadTimeWeaver for a particular ApplicationContext can be as easy as adding one

line. (Please note that you almost certainly will need to be using an ApplicationContext as your

Spring container - typically a BeanFactory will not be enough because the LTW support makes use

of BeanFactoryPostProcessors.)

To enable the Spring Framework’s LTW support, you need to configure a LoadTimeWeaver, which

typically is done using the @EnableLoadTimeWeaving annotation.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 239

@Configuration

@EnableLoadTimeWeaving

public class AppConfig {

}

Alternatively, if you prefer XML based configuration, use the <context:load-time-weaver/>

element. Note that the element is defined in the context namespace.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:load-time-weaver/>

</beans>

The above configuration will define and register a number of LTW-specific infrastructure beans for

you automatically, such as a LoadTimeWeaver and an AspectJWeavingEnabler. The default

LoadTimeWeaver is the DefaultContextLoadTimeWeaver class, which attempts to decorate

an automatically detected LoadTimeWeaver: the exact type of LoadTimeWeaver that will be

automatically detected is dependent upon your runtime environment (summarized in the following table).

Table 9.1. DefaultContextLoadTimeWeaver LoadTimeWeavers

Runtime Environment LoadTimeWeaver implementation

Running in BEA’s Weblogic 10 WebLogicLoadTimeWeaver

Running in IBM WebSphere Application Server 7 WebSphereLoadTimeWeaver

Running in GlassFish GlassFishLoadTimeWeaver

Running in JBoss AS JBossLoadTimeWeaver

JVM started with Spring

InstrumentationSavingAgent (java -

javaagent:path/to/spring-instrument.jar)

InstrumentationLoadTimeWeaver

Fallback, expecting the underlying ClassLoader

to follow common conventions (e.g. applicable to

TomcatInstrumentableClassLoader and

Resin)

ReflectiveLoadTimeWeaver

Note that these are just the LoadTimeWeavers that are autodetected when using

the DefaultContextLoadTimeWeaver: it is of course possible to specify exactly which

LoadTimeWeaver implementation that you wish to use.

To specify a specific LoadTimeWeaver with Java configuration implement the

LoadTimeWeavingConfigurer interface and override the getLoadTimeWeaver() method:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 240

@Configuration

@EnableLoadTimeWeaving

public class AppConfig implements LoadTimeWeavingConfigurer {

@Override

public LoadTimeWeaver getLoadTimeWeaver() {

return new ReflectiveLoadTimeWeaver();

}

If you are using XML based configuration you can specify the fully-qualified classname as the value of

the weaver-class attribute on the <context:load-time-weaver/> element:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:load-time-weaver

weaver-class="org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver"/>

</beans>

The LoadTimeWeaver that is defined and registered by the configuration can be later retrieved

from the Spring container using the well-known name loadTimeWeaver. Remember that the

LoadTimeWeaver exists just as a mechanism for Spring’s LTW infrastructure to add one or

more ClassFileTransformers. The actual ClassFileTransformer that does the LTW is the

ClassPreProcessorAgentAdapter (from the org.aspectj.weaver.loadtime package) class.

See the class-level javadocs of the ClassPreProcessorAgentAdapter class for further details,

because the specifics of how the weaving is actually effected is beyond the scope of this section.

There is one final attribute of the configuration left to discuss: the aspectjWeaving attribute (or

aspectj-weaving if you are using XML). This is a simple attribute that controls whether LTW is

enabled or not; it is as simple as that. It accepts one of three possible values, summarized below, with

the default value being autodetect if the attribute is not present.

Table 9.2. AspectJ weaving attribute values

Annotation Value XML Value Explanation

ENABLED on AspectJ weaving is on, and

aspects will be woven at load-

time as appropriate.

DISABLED off LTW is off… no aspect will be

woven at load-time.

AUTODETECT autodetect If the Spring LTW infrastructure

can find at least one META-

INF/aop.xml file, then

AspectJ weaving is on, else it is

off. This is the default value.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 241

Environment-specific configuration

This last section contains any additional settings and configuration that you will need when using

Spring’s LTW support in environments such as application servers and web containers.

Tomcat

Apache Tomcat's default class loader does not support class transformation which is

why Spring provides an enhanced implementation that addresses this need. Named

TomcatInstrumentableClassLoader, the loader works on Tomcat 5.0 and above and can be

registered individually for each web application as follows:

• Tomcat 6.0.x or higher

• Copy org.springframework.instrument.tomcat.jar into $CATALINA_HOME/lib, where

$CATALINA_HOME represents the root of the Tomcat installation)

• Instruct Tomcat to use the custom class loader (instead of the default) by editing the web application

context file:

<Loader

loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader"/>

</Context>

Apache Tomcat (6.0+) supports several context locations:

• server configuration file - $CATALINA_HOME/conf/server.xml

• default context configuration - $CATALINA_HOME/conf/context.xml - that affects all deployed web

applications

• per-web application configuration which can be deployed either on the server-side at

$CATALINA_HOME/conf/[enginename]/[hostname]/[webapp]-context.xml or embedded inside the

web-app archive at META-INF/context.xml

For efficiency, the embedded per-web-app configuration style is recommended because it will impact

only applications that use the custom class loader and does not require any changes to the server

configuration. See the Tomcat 6.0.x documentation for more details about available context locations.

Alternatively, consider the use of the Spring-provided generic VM agent, to be specified in Tomcat’s

launch script (see above). This will make instrumentation available to all deployed web applications, no

matter what ClassLoader they happen to run on.

WebLogic, WebSphere, Resin, GlassFish, JBoss

Recent versions of WebLogic Server (version 10 and above), IBM WebSphere Application Server

(version 7 and above), Resin (3.1 and above) and JBoss (6.x or above) provide a ClassLoader

that is capable of local instrumentation. Spring’s native LTW leverages such ClassLoaders to enable

AspectJ weaving. You can enable LTW by simply activating load-time weaving as described earlier.

Specifically, you do not need to modify the launch script to add -javaagent:path/to/spring-

instrument.jar.

Note that GlassFish instrumentation-capable ClassLoader is available only in its EAR environment. For

GlassFish web applications, follow the Tomcat setup instructions as outlined above.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 242

Note that on JBoss 6.x, the app server scanning needs to be disabled to prevent it from loading the

classes before the application actually starts. A quick workaround is to add to your artifact a file named

WEB-INF/jboss-scanning.xml with the following content:

Generic Java applications

When class instrumentation is required in environments that do not support or are not supported

by the existing LoadTimeWeaver implementations, a JDK agent can be the only solution. For

such cases, Spring provides InstrumentationLoadTimeWeaver, which requires a Spring-specific

(but very general) VM agent, org.springframework.instrument-{version}.jar (previously

named spring-agent.jar).

To use it, you must start the virtual machine with the Spring agent, by supplying the following JVM

options:

-javaagent:/path/to/org.springframework.instrument-{version}.jar

Note that this requires modification of the VM launch script which may prevent you from using this in

application server environments (depending on your operation policies). Additionally, the JDK agent will

instrument the entire VM which can prove expensive.

For performance reasons, it is recommended to use this configuration only if your target environment

(such as Jetty) does not have (or does not support) a dedicated LTW.

9.9 Further Resources

More information on AspectJ can be found on the AspectJ website.

The book Eclipse AspectJ by Adrian Colyer et. al. (Addison-Wesley, 2005) provides a comprehensive

introduction and reference for the AspectJ language.

The book AspectJ in Action by Ramnivas Laddad (Manning, 2003) comes highly recommended; the

focus of the book is on AspectJ, but a lot of general AOP themes are explored (in some depth).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 243

10. Spring AOP APIs

10.1 Introduction

The previous chapter described the Spring’s support for AOP using @AspectJ and schema-based

aspect definitions. In this chapter we discuss the lower-level Spring AOP APIs and the AOP support

used in Spring 1.2 applications. For new applications, we recommend the use of the Spring 2.0 and later

AOP support described in the previous chapter, but when working with existing applications, or when

reading books and articles, you may come across Spring 1.2 style examples. Spring 4.0 is backwards

compatible with Spring 1.2 and everything described in this chapter is fully supported in Spring 4.0.

10.2 Pointcut API in Spring

Let’s look at how Spring handles the crucial pointcut concept.

Concepts

Spring’s pointcut model enables pointcut reuse independent of advice types. It’s possible to target

different advice using the same pointcut.

The org.springframework.aop.Pointcut interface is the central interface, used to target advices

to particular classes and methods. The complete interface is shown below:

public interface Pointcut {

ClassFilter getClassFilter();

MethodMatcher getMethodMatcher();

}

Splitting the Pointcut interface into two parts allows reuse of class and method matching parts, and

fine-grained composition operations (such as performing a "union" with another method matcher).

The ClassFilter interface is used to restrict the pointcut to a given set of target classes. If the

matches() method always returns true, all target classes will be matched:

public interface ClassFilter {

boolean matches(Class clazz);

}

The MethodMatcher interface is normally more important. The complete interface is shown below:

public interface MethodMatcher {

boolean matches(Method m, Class targetClass);

boolean isRuntime();

boolean matches(Method m, Class targetClass, Object[] args);

}

The matches(Method, Class) method is used to test whether this pointcut will ever match a given

method on a target class. This evaluation can be performed when an AOP proxy is created, to avoid the

need for a test on every method invocation. If the 2-argument matches method returns true for a given

method, and the isRuntime() method for the MethodMatcher returns true, the 3-argument matches

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 244

method will be invoked on every method invocation. This enables a pointcut to look at the arguments

passed to the method invocation immediately before the target advice is to execute.

Most MethodMatchers are static, meaning that their isRuntime() method returns false. In this case,

the 3-argument matches method will never be invoked.

Tip

If possible, try to make pointcuts static, allowing the AOP framework to cache the results of pointcut

evaluation when an AOP proxy is created.

Operations on pointcuts

Spring supports operations on pointcuts: notably, union and intersection.

• Union means the methods that either pointcut matches.

• Intersection means the methods that both pointcuts match.

• Union is usually more useful.

• Pointcuts can be composed using the static methods in the

org.springframework.aop.support.Pointcuts class, or using the ComposablePointcut class in the same

package. However, using AspectJ pointcut expressions is usually a simpler approach.

AspectJ expression pointcuts

Since 2.0, the most important type of pointcut used by Spring is

org.springframework.aop.aspectj.AspectJExpressionPointcut. This is a pointcut that

uses an AspectJ supplied library to parse an AspectJ pointcut expression string.

See the previous chapter for a discussion of supported AspectJ pointcut primitives.

Convenience pointcut implementations

Spring provides several convenient pointcut implementations. Some can be used out of the box; others

are intended to be subclassed in application-specific pointcuts.

Static pointcuts

Static pointcuts are based on method and target class, and cannot take into account the method’s

arguments. Static pointcuts are sufficient - and best - for most usages. It’s possible for Spring to evaluate

a static pointcut only once, when a method is first invoked: after that, there is no need to evaluate the

pointcut again with each method invocation.

Let’s consider some static pointcut implementations included with Spring.

Regular expression pointcuts

One obvious way to specify static pointcuts is regular expressions. Several AOP frameworks besides

Spring make this possible. org.springframework.aop.support.JdkRegexpMethodPointcut

is a generic regular expression pointcut, using the regular expression support in JDK 1.4+.

Using the JdkRegexpMethodPointcut class, you can provide a list of pattern Strings. If any of these

is a match, the pointcut will evaluate to true. (So the result is effectively the union of these pointcuts.)

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 245

The usage is shown below:

<bean id="settersAndAbsquatulatePointcut"

class="org.springframework.aop.support.JdkRegexpMethodPointcut">

<list>

<value>.*absquatulate</value>

</list>

</property>

</bean>

Spring provides a convenience class, RegexpMethodPointcutAdvisor, that allows us to

also reference an Advice (remember that an Advice can be an interceptor, before advice,

throws advice etc.). Behind the scenes, Spring will use a JdkRegexpMethodPointcut. Using

RegexpMethodPointcutAdvisor simplifies wiring, as the one bean encapsulates both pointcut and

advice, as shown below:

<bean id="settersAndAbsquatulateAdvisor"

class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">

</property>

<list>

<value>.*absquatulate</value>

</list>

</property>

</bean>

RegexpMethodPointcutAdvisor can be used with any Advice type.

Attribute-driven pointcuts

An important type of static pointcut is a metadata-driven pointcut. This uses the values of metadata

attributes: typically, source-level metadata.

Dynamic pointcuts

Dynamic pointcuts are costlier to evaluate than static pointcuts. They take into account method

arguments, as well as static information. This means that they must be evaluated with every method

invocation; the result cannot be cached, as arguments will vary.

The main example is the control flow pointcut.

Control flow pointcuts

Spring control flow pointcuts are conceptually similar to AspectJ cflow pointcuts, although less

powerful. (There is currently no way to specify that a pointcut executes below a join point

matched by another pointcut.) A control flow pointcut matches the current call stack. For

example, it might fire if the join point was invoked by a method in the com.mycompany.web

package, or by the SomeCaller class. Control flow pointcuts are specified using the

org.springframework.aop.support.ControlFlowPointcut class.

Note

Control flow pointcuts are significantly more expensive to evaluate at runtime than even other

dynamic pointcuts. In Java 1.4, the cost is about 5 times that of other dynamic pointcuts.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 246

Pointcut superclasses

Spring provides useful pointcut superclasses to help you to implement your own pointcuts.

Because static pointcuts are most useful, you’ll probably subclass StaticMethodMatcherPointcut, as

shown below. This requires implementing just one abstract method (although it’s possible to override

other methods to customize behavior):

class TestStaticPointcut extends StaticMethodMatcherPointcut {

public boolean matches(Method m, Class targetClass) {

// return true if custom criteria match

}

There are also superclasses for dynamic pointcuts.

You can use custom pointcuts with any advice type in Spring 1.0 RC2 and above.

Custom pointcuts

Because pointcuts in Spring AOP are Java classes, rather than language features (as in AspectJ)

it’s possible to declare custom pointcuts, whether static or dynamic. Custom pointcuts in Spring can

be arbitrarily complex. However, using the AspectJ pointcut expression language is recommended if

possible.

Note

Later versions of Spring may offer support for "semantic pointcuts" as offered by JAC: for example,

"all methods that change instance variables in the target object."

10.3 Advice API in Spring

Let’s now look at how Spring AOP handles advice.

Advice lifecycles

Each advice is a Spring bean. An advice instance can be shared across all advised objects, or unique

to each advised object. This corresponds to per-class or per-instance advice.

Per-class advice is used most often. It is appropriate for generic advice such as transaction advisors.

These do not depend on the state of the proxied object or add new state; they merely act on the method

and arguments.

Per-instance advice is appropriate for introductions, to support mixins. In this case, the advice adds

state to the proxied object.

It’s possible to use a mix of shared and per-instance advice in the same AOP proxy.

Advice types in Spring

Spring provides several advice types out of the box, and is extensible to support arbitrary advice types.

Let us look at the basic concepts and standard advice types.

Interception around advice

The most fundamental advice type in Spring is interception around advice.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 247

Spring is compliant with the AOP Alliance interface for around advice using method interception.

MethodInterceptors implementing around advice should implement the following interface:

public interface MethodInterceptor extends Interceptor {

Object invoke(MethodInvocation invocation) throws Throwable;

}

The MethodInvocation argument to the invoke() method exposes the method being invoked; the

target join point; the AOP proxy; and the arguments to the method. The invoke() method should return

the invocation’s result: the return value of the join point.

A simple MethodInterceptor implementation looks as follows:

public class DebugInterceptor implements MethodInterceptor {

public Object invoke(MethodInvocation invocation) throws Throwable {

System.out.println("Before: invocation=[" + invocation + "]");

Object rval = invocation.proceed();

System.out.println("Invocation returned");

return rval;

}

Note the call to the MethodInvocation’s proceed() method. This proceeds down the interceptor chain

towards the join point. Most interceptors will invoke this method, and return its return value. However,

a MethodInterceptor, like any around advice, can return a different value or throw an exception rather

than invoke the proceed method. However, you don’t want to do this without good reason!

Note

MethodInterceptors offer interoperability with other AOP Alliance-compliant AOP

implementations. The other advice types discussed in the remainder of this section implement

common AOP concepts, but in a Spring-specific way. While there is an advantage in using the

most specific advice type, stick with MethodInterceptor around advice if you are likely to want

to run the aspect in another AOP framework. Note that pointcuts are not currently interoperable

between frameworks, and the AOP Alliance does not currently define pointcut interfaces.

Before advice

A simpler advice type is a before advice. This does not need a MethodInvocation object, since it will

only be called before entering the method.

The main advantage of a before advice is that there is no need to invoke the proceed() method, and

therefore no possibility of inadvertently failing to proceed down the interceptor chain.

The MethodBeforeAdvice interface is shown below. (Spring’s API design would allow for field before

advice, although the usual objects apply to field interception and it’s unlikely that Spring will ever

implement it).

public interface MethodBeforeAdvice extends BeforeAdvice {

void before(Method m, Object[] args, Object target) throws Throwable;

}

Note the return type is void. Before advice can insert custom behavior before the join point executes, but

cannot change the return value. If a before advice throws an exception, this will abort further execution

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 248

of the interceptor chain. The exception will propagate back up the interceptor chain. If it is unchecked,

or on the signature of the invoked method, it will be passed directly to the client; otherwise it will be

wrapped in an unchecked exception by the AOP proxy.

An example of a before advice in Spring, which counts all method invocations:

public class CountingBeforeAdvice implements MethodBeforeAdvice {

private int count;

public void before(Method m, Object[] args, Object target) throws Throwable {

++count;

}

public int getCount() {

return count;

}

Tip

Before advice can be used with any pointcut.

Throws advice

Throws advice is invoked after the return of the join point if the join point threw an exception. Spring offers

typed throws advice. Note that this means that the org.springframework.aop.ThrowsAdvice

interface does not contain any methods: It is a tag interface identifying that the given object implements

one or more typed throws advice methods. These should be in the form of:

afterThrowing([Method, args, target], subclassOfThrowable)

Only the last argument is required. The method signatures may have either one or four arguments,

depending on whether the advice method is interested in the method and arguments. The following

classes are examples of throws advice.

The advice below is invoked if a RemoteException is thrown (including subclasses):

public class RemoteThrowsAdvice implements ThrowsAdvice {

public void afterThrowing(RemoteException ex) throws Throwable {

// Do something with remote exception

}

The following advice is invoked if a ServletException is thrown. Unlike the above advice, it declares

4 arguments, so that it has access to the invoked method, method arguments and target object:

public class ServletThrowsAdviceWithArguments implements ThrowsAdvice {

public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) {

// Do something with all arguments

}

The final example illustrates how these two methods could be used in a single class, which handles

both RemoteException and ServletException. Any number of throws advice methods can be

combined in a single class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 249

public static class CombinedThrowsAdvice implements ThrowsAdvice {

public void afterThrowing(RemoteException ex) throws Throwable {

// Do something with remote exception

}

public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) {

// Do something with all arguments

}

Note

If a throws-advice method throws an exception itself, it will override the original exception

(i.e. change the exception thrown to the user). The overriding exception will typically be a

RuntimeException; this is compatible with any method signature. However, if a throws-advice

method throws a checked exception, it will have to match the declared exceptions of the target

method and is hence to some degree coupled to specific target method signatures. Do not throw

an undeclared checked exception that is incompatible with the target method’s signature!

Tip

Throws advice can be used with any pointcut.

After Returning advice

An after returning advice in Spring must implement the org.springframework.aop.AfterReturningAdvice

interface, shown below:

public interface AfterReturningAdvice extends Advice {

void afterReturning(Object returnValue, Method m, Object[] args, Object target)

throws Throwable;

}

An after returning advice has access to the return value (which it cannot modify), invoked method,

methods arguments and target.

The following after returning advice counts all successful method invocations that have not thrown

exceptions:

public class CountingAfterReturningAdvice implements AfterReturningAdvice {

private int count;

public void afterReturning(Object returnValue, Method m, Object[] args, Object target)

throws Throwable {

++count;

}

public int getCount() {

return count;

}

This advice doesn’t change the execution path. If it throws an exception, this will be thrown up the

interceptor chain instead of the return value.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 250

Tip

After returning advice can be used with any pointcut.

Introduction advice

Spring treats introduction advice as a special kind of interception advice.

Introduction requires an IntroductionAdvisor, and an IntroductionInterceptor,

implementing the following interface:

public interface IntroductionInterceptor extends MethodInterceptor {

boolean implementsInterface(Class intf);

}

The invoke() method inherited from the AOP Alliance MethodInterceptor interface must

implement the introduction: that is, if the invoked method is on an introduced interface, the introduction

interceptor is responsible for handling the method call - it cannot invoke proceed().

Introduction advice cannot be used with any pointcut, as it applies only at class, rather than method,

level. You can only use introduction advice with the IntroductionAdvisor, which has the following

methods:

public interface IntroductionAdvisor extends Advisor, IntroductionInfo {

ClassFilter getClassFilter();

void validateInterfaces() throws IllegalArgumentException;

}

public interface IntroductionInfo {

Class[] getInterfaces();

}

There is no MethodMatcher, and hence no Pointcut, associated with introduction advice. Only class

filtering is logical.

The getInterfaces() method returns the interfaces introduced by this advisor.

The validateInterfaces() method is used internally to see whether or not the introduced interfaces

can be implemented by the configured IntroductionInterceptor.

Let’s look at a simple example from the Spring test suite. Let’s suppose we want to introduce the

following interface to one or more objects:

public interface Lockable {

void lock();

void unlock();

boolean locked();

}

This illustrates a mixin. We want to be able to cast advised objects to Lockable, whatever their type,

and call lock and unlock methods. If we call the lock() method, we want all setter methods to throw a

LockedException. Thus we can add an aspect that provides the ability to make objects immutable,

without them having any knowledge of it: a good example of AOP.

Firstly, we’ll need an IntroductionInterceptor that does the heavy lifting. In this case, we

extend the org.springframework.aop.support.DelegatingIntroductionInterceptor

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 251

convenience class. We could implement IntroductionInterceptor directly, but using

DelegatingIntroductionInterceptor is best for most cases.

The DelegatingIntroductionInterceptor is designed to delegate an introduction to an actual

implementation of the introduced interface(s), concealing the use of interception to do so. The

delegate can be set to any object using a constructor argument; the default delegate (when the

no-arg constructor is used) is this. Thus in the example below, the delegate is the LockMixin

subclass of DelegatingIntroductionInterceptor. Given a delegate (by default itself), a

DelegatingIntroductionInterceptor instance looks for all interfaces implemented by the

delegate (other than IntroductionInterceptor), and will support introductions against any of them. It’s

possible for subclasses such as LockMixin to call the suppressInterface(Class intf) method

to suppress interfaces that should not be exposed. However, no matter how many interfaces an

IntroductionInterceptor is prepared to support, the IntroductionAdvisor used will control

which interfaces are actually exposed. An introduced interface will conceal any implementation of the

same interface by the target.

Thus LockMixin extends DelegatingIntroductionInterceptor and implements Lockable

itself. The superclass automatically picks up that Lockable can be supported for introduction, so we

don’t need to specify that. We could introduce any number of interfaces in this way.

Note the use of the locked instance variable. This effectively adds additional state to that held in the

target object.

public class LockMixin extends DelegatingIntroductionInterceptor implements Lockable {

private boolean locked;

public void lock() {

this.locked = true;

}

public void unlock() {

this.locked = false;

}

public boolean locked() {

return this.locked;

}

public Object invoke(MethodInvocation invocation) throws Throwable {

if (locked() && invocation.getMethod().getName().indexOf("set") == 0) {

throw new LockedException();

}

return super.invoke(invocation);

}

Often it isn’t necessary to override the invoke() method: the

DelegatingIntroductionInterceptor implementation - which calls the delegate method if the

method is introduced, otherwise proceeds towards the join point - is usually sufficient. In the present

case, we need to add a check: no setter method can be invoked if in locked mode.

The introduction advisor required is simple. All it needs to do is hold a distinct LockMixin instance, and

specify the introduced interfaces - in this case, just Lockable. A more complex example might take a

reference to the introduction interceptor (which would be defined as a prototype): in this case, there’s

no configuration relevant for a LockMixin, so we simply create it using new.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 252

public class LockMixinAdvisor extends DefaultIntroductionAdvisor {

public LockMixinAdvisor() {

super(new LockMixin(), Lockable.class);

}

We can apply this advisor very simply: it requires no configuration. (However, it is necessary: It’s

impossible to use an IntroductionInterceptor without an IntroductionAdvisor.) As usual with

introductions, the advisor must be per-instance, as it is stateful. We need a different instance of

LockMixinAdvisor, and hence LockMixin, for each advised object. The advisor comprises part of

the advised object’s state.

We can apply this advisor programmatically, using the Advised.addAdvisor() method, or (the

recommended way) in XML configuration, like any other advisor. All proxy creation choices discussed

below, including "auto proxy creators," correctly handle introductions and stateful mixins.

10.4 Advisor API in Spring

In Spring, an Advisor is an aspect that contains just a single advice object associated with a pointcut

expression.

Apart from the special case of introductions, any advisor can be used with any advice.

org.springframework.aop.support.DefaultPointcutAdvisor is the most commonly used

advisor class. For example, it can be used with a MethodInterceptor, BeforeAdvice or

ThrowsAdvice.

It is possible to mix advisor and advice types in Spring in the same AOP proxy. For example, you could

use a interception around advice, throws advice and before advice in one proxy configuration: Spring

will automatically create the necessary interceptor chain.

10.5 Using the ProxyFactoryBean to create AOP proxies

If you’re using the Spring IoC container (an ApplicationContext or BeanFactory) for your business objects

- and you should be! - you will want to use one of Spring’s AOP FactoryBeans. (Remember that a factory

bean introduces a layer of indirection, enabling it to create objects of a different type.)

Note

The Spring AOP support also uses factory beans under the covers.

The basic way to create an AOP proxy in Spring is to use the

org.springframework.aop.framework.ProxyFactoryBean. This gives complete control over the pointcuts

and advice that will apply, and their ordering. However, there are simpler options that are preferable if

you don’t need such control.

Basics

The ProxyFactoryBean, like other Spring FactoryBean implementations, introduces a level of

indirection. If you define a ProxyFactoryBean with name foo, what objects referencing foo see

is not the ProxyFactoryBean instance itself, but an object created by the ProxyFactoryBean's

implementation of the getObject() method. This method will create an AOP proxy wrapping a target

object.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 253

One of the most important benefits of using a ProxyFactoryBean or another IoC-aware class to create

AOP proxies, is that it means that advices and pointcuts can also be managed by IoC. This is a powerful

feature, enabling certain approaches that are hard to achieve with other AOP frameworks. For example,

an advice may itself reference application objects (besides the target, which should be available in any

AOP framework), benefiting from all the pluggability provided by Dependency Injection.

JavaBean properties

In common with most FactoryBean implementations provided with Spring, the ProxyFactoryBean

class is itself a JavaBean. Its properties are used to:

• Specify the target you want to proxy.

• Specify whether to use CGLIB (see below and also the section called “JDK- and CGLIB-based

proxies”).

Some key properties are inherited from org.springframework.aop.framework.ProxyConfig

(the superclass for all AOP proxy factories in Spring). These key properties include:

•proxyTargetClass: true if the target class is to be proxied, rather than the target class' interfaces.

If this property value is set to true, then CGLIB proxies will be created (but see also the section

called “JDK- and CGLIB-based proxies”).

•optimize: controls whether or not aggressive optimizations are applied to proxies created via CGLIB.

One should not blithely use this setting unless one fully understands how the relevant AOP proxy

handles optimization. This is currently used only for CGLIB proxies; it has no effect with JDK dynamic

proxies.

•frozen: if a proxy configuration is frozen, then changes to the configuration are no longer allowed.

This is useful both as a slight optimization and for those cases when you don’t want callers to be able

to manipulate the proxy (via the Advised interface) after the proxy has been created. The default

value of this property is false, so changes such as adding additional advice are allowed.

•exposeProxy: determines whether or not the current proxy should be exposed in a ThreadLocal

so that it can be accessed by the target. If a target needs to obtain the proxy and the exposeProxy

property is set to true, the target can use the AopContext.currentProxy() method.

Other properties specific to ProxyFactoryBean include:

•proxyInterfaces: array of String interface names. If this isn’t supplied, a CGLIB proxy for the target

class will be used (but see also the section called “JDK- and CGLIB-based proxies”).

•interceptorNames: String array of Advisor, interceptor or other advice names to apply. Ordering

is significant, on a first come-first served basis. That is to say that the first interceptor in the list will

be the first to be able to intercept the invocation.

The names are bean names in the current factory, including bean names from ancestor factories. You

can’t mention bean references here since doing so would result in the ProxyFactoryBean ignoring

the singleton setting of the advice.

You can append an interceptor name with an asterisk ( *). This will result in the application of all advisor

beans with names starting with the part before the asterisk to be applied. An example of using this

feature can be found in the section called “Using global advisors”.

• singleton: whether or not the factory should return a single object, no matter how often the

getObject() method is called. Several FactoryBean implementations offer such a method. The

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 254

default value is true. If you want to use stateful advice - for example, for stateful mixins - use prototype

advices along with a singleton value of false.

JDK- and CGLIB-based proxies

This section serves as the definitive documentation on how the ProxyFactoryBean chooses to create

one of either a JDK- and CGLIB-based proxy for a particular target object (that is to be proxied).

Note

The behavior of the ProxyFactoryBean with regard to creating JDK- or CGLIB-based

proxies changed between versions 1.2.x and 2.0 of Spring. The ProxyFactoryBean

now exhibits similar semantics with regard to auto-detecting interfaces as those of the

TransactionProxyFactoryBean class.

If the class of a target object that is to be proxied (hereafter simply referred to as the target class) doesn’t

implement any interfaces, then a CGLIB-based proxy will be created. This is the easiest scenario,

because JDK proxies are interface based, and no interfaces means JDK proxying isn’t even possible.

One simply plugs in the target bean, and specifies the list of interceptors via the interceptorNames

property. Note that a CGLIB-based proxy will be created even if the proxyTargetClass property of

the ProxyFactoryBean has been set to false. (Obviously this makes no sense, and is best removed

from the bean definition because it is at best redundant, and at worst confusing.)

If the target class implements one (or more) interfaces, then the type of proxy that is created depends

on the configuration of the ProxyFactoryBean.

If the proxyTargetClass property of the ProxyFactoryBean has been set to true, then a CGLIB-

based proxy will be created. This makes sense, and is in keeping with the principle of least surprise.

Even if the proxyInterfaces property of the ProxyFactoryBean has been set to one or more fully

qualified interface names, the fact that the proxyTargetClass property is set to true will cause

CGLIB-based proxying to be in effect.

If the proxyInterfaces property of the ProxyFactoryBean has been set to one or more fully

qualified interface names, then a JDK-based proxy will be created. The created proxy will implement all

of the interfaces that were specified in the proxyInterfaces property; if the target class happens to

implement a whole lot more interfaces than those specified in the proxyInterfaces property, that is

all well and good but those additional interfaces will not be implemented by the returned proxy.

If the proxyInterfaces property of the ProxyFactoryBean has not been set, but the target class

does implement one (or more) interfaces, then the ProxyFactoryBean will auto-detect the fact that the

target class does actually implement at least one interface, and a JDK-based proxy will be created. The

interfaces that are actually proxied will be all of the interfaces that the target class implements; in effect,

this is the same as simply supplying a list of each and every interface that the target class implements

to the proxyInterfaces property. However, it is significantly less work, and less prone to typos.

Proxying interfaces

Let’s look at a simple example of ProxyFactoryBean in action. This example involves:

• A target bean that will be proxied. This is the "personTarget" bean definition in the example below.

• An Advisor and an Interceptor used to provide advice.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 255

• An AOP proxy bean definition specifying the target object (the personTarget bean) and the interfaces

to proxy, along with the advices to apply.

</bean>

</bean>

</bean>

<bean id="person"

class="org.springframework.aop.framework.ProxyFactoryBean">

<list>

<value>myAdvisor</value>

<value>debugInterceptor</value>

</list>

</property>

</bean>

Note that the interceptorNames property takes a list of String: the bean names of the interceptor or

advisors in the current factory. Advisors, interceptors, before, after returning and throws advice objects

can be used. The ordering of advisors is significant.

Note

You might be wondering why the list doesn’t hold bean references. The reason for this is that if

the ProxyFactoryBean’s singleton property is set to false, it must be able to return independent

proxy instances. If any of the advisors is itself a prototype, an independent instance would need

to be returned, so it’s necessary to be able to obtain an instance of the prototype from the factory;

holding a reference isn’t sufficient.

The "person" bean definition above can be used in place of a Person implementation, as follows:

Person person = (Person) factory.getBean("person");

Other beans in the same IoC context can express a strongly typed dependency on it, as with an ordinary

Java object:

</bean>

The PersonUser class in this example would expose a property of type Person. As far as it’s concerned,

the AOP proxy can be used transparently in place of a "real" person implementation. However, its class

would be a dynamic proxy class. It would be possible to cast it to the Advised interface (discussed

below).

It’s possible to conceal the distinction between target and proxy using an anonymous inner bean,

as follows. Only the ProxyFactoryBean definition is different; the advice is included only for

completeness:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 256

</bean>

</bean>

</property>

<list>

<value>myAdvisor</value>

<value>debugInterceptor</value>

</list>

</property>

</bean>

This has the advantage that there’s only one object of type Person: useful if we want to prevent users

of the application context from obtaining a reference to the un-advised object, or need to avoid any

ambiguity with Spring IoC autowiring. There’s also arguably an advantage in that the ProxyFactoryBean

definition is self-contained. However, there are times when being able to obtain the un-advised target

from the factory might actually be an advantage: for example, in certain test scenarios.

Proxying classes

What if you need to proxy a class, rather than one or more interfaces?

Imagine that in our example above, there was no Person interface: we needed to advise a class called

Person that didn’t implement any business interface. In this case, you can configure Spring to use

CGLIB proxying, rather than dynamic proxies. Simply set the proxyTargetClass property on the

ProxyFactoryBean above to true. While it’s best to program to interfaces, rather than classes, the ability

to advise classes that don’t implement interfaces can be useful when working with legacy code. (In

general, Spring isn’t prescriptive. While it makes it easy to apply good practices, it avoids forcing a

particular approach.)

If you want to, you can force the use of CGLIB in any case, even if you do have interfaces.

CGLIB proxying works by generating a subclass of the target class at runtime. Spring configures this

generated subclass to delegate method calls to the original target: the subclass is used to implement

the Decorator pattern, weaving in the advice.

CGLIB proxying should generally be transparent to users. However, there are some issues to consider:

•Final methods can’t be advised, as they can’t be overridden.

• There is no need to add CGLIB to your classpath. As of Spring 3.2, CGLIB is repackaged and included

in the spring-core JAR. In other words, CGLIB-based AOP will work "out of the box" just as do JDK

dynamic proxies.

There’s little performance difference between CGLIB proxying and dynamic proxies. As of Spring 1.0,

dynamic proxies are slightly faster. However, this may change in the future. Performance should not be

a decisive consideration in this case.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 257

Using global advisors

By appending an asterisk to an interceptor name, all advisors with bean names matching the part before

the asterisk, will be added to the advisor chain. This can come in handy if you need to add a standard

set of global advisors:

<list>

<value>global*</value>

</list>

</property>

</bean>

<bean id="global_performance" class="org.springframework.aop.interceptor.PerformanceMonitorInterceptor"/

10.6 Concise proxy definitions

Especially when defining transactional proxies, you may end up with many similar proxy definitions. The

use of parent and child bean definitions, along with inner bean definitions, can result in much cleaner

and more concise proxy definitions.

First a parent, template, bean definition is created for the proxy:

<bean id="txProxyTemplate" abstract="true"

class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">

<props>

<prop key="*">PROPAGATION_REQUIRED</prop>

</props>

</property>

</bean>

This will never be instantiated itself, so may actually be incomplete. Then each proxy which needs to be

created is just a child bean definition, which wraps the target of the proxy as an inner bean definition,

since the target will never be used on its own anyway.

</bean>

</property>

</bean>

It is of course possible to override properties from the parent template, such as in this case, the

transaction propagation settings:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 258

</bean>

</property>

<props>

<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>

<prop key="find*">PROPAGATION_REQUIRED,readOnly</prop>

<prop key="load*">PROPAGATION_REQUIRED,readOnly</prop>

<prop key="store*">PROPAGATION_REQUIRED</prop>

</props>

</property>

</bean>

Note that in the example above, we have explicitly marked the parent bean definition as abstract by

using the abstract attribute, as described previously, so that it may not actually ever be instantiated.

Application contexts (but not simple bean factories) will by default pre-instantiate all singletons. It is

therefore important (at least for singleton beans) that if you have a (parent) bean definition which you

intend to use only as a template, and this definition specifies a class, you must make sure to set the

abstract attribute to true, otherwise the application context will actually try to pre-instantiate it.

10.7 Creating AOP proxies programmatically with the

ProxyFactory

It’s easy to create AOP proxies programmatically using Spring. This enables you to use Spring AOP

without dependency on Spring IoC.

The following listing shows creation of a proxy for a target object, with one interceptor and one advisor.

The interfaces implemented by the target object will automatically be proxied:

ProxyFactory factory = new ProxyFactory(myBusinessInterfaceImpl);

factory.addAdvice(myMethodInterceptor);

factory.addAdvisor(myAdvisor);

MyBusinessInterface tb = (MyBusinessInterface) factory.getProxy();

The first step is to construct an object of type

org.springframework.aop.framework.ProxyFactory. You can create this with a target object,

as in the above example, or specify the interfaces to be proxied in an alternate constructor.

You can add advices (with interceptors as a specialized kind of advice) and/or advisors, and manipulate

them for the life of the ProxyFactory. If you add an IntroductionInterceptionAroundAdvisor, you can

cause the proxy to implement additional interfaces.

There are also convenience methods on ProxyFactory (inherited from AdvisedSupport) which allow

you to add other advice types such as before and throws advice. AdvisedSupport is the superclass of

both ProxyFactory and ProxyFactoryBean.

Tip

Integrating AOP proxy creation with the IoC framework is best practice in most applications. We

recommend that you externalize configuration from Java code with AOP, as in general.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 259

10.8 Manipulating advised objects

However you create AOP proxies, you can manipulate them using the

org.springframework.aop.framework.Advised interface. Any AOP proxy can be cast to this

interface, whichever other interfaces it implements. This interface includes the following methods:

Advisor[] getAdvisors();

void addAdvice(Advice advice) throws AopConfigException;

void addAdvice(int pos, Advice advice) throws AopConfigException;

void addAdvisor(Advisor advisor) throws AopConfigException;

void addAdvisor(int pos, Advisor advisor) throws AopConfigException;

int indexOf(Advisor advisor);

boolean removeAdvisor(Advisor advisor) throws AopConfigException;

void removeAdvisor(int index) throws AopConfigException;

boolean replaceAdvisor(Advisor a, Advisor b) throws AopConfigException;

boolean isFrozen();

The getAdvisors() method will return an Advisor for every advisor, interceptor or other advice

type that has been added to the factory. If you added an Advisor, the returned advisor at this

index will be the object that you added. If you added an interceptor or other advice type, Spring

will have wrapped this in an advisor with a pointcut that always returns true. Thus if you added a

MethodInterceptor, the advisor returned for this index will be an DefaultPointcutAdvisor

returning your MethodInterceptor and a pointcut that matches all classes and methods.

The addAdvisor() methods can be used to add any Advisor. Usually the advisor holding pointcut and

advice will be the generic DefaultPointcutAdvisor, which can be used with any advice or pointcut

(but not for introductions).

By default, it’s possible to add or remove advisors or interceptors even once a proxy has been created.

The only restriction is that it’s impossible to add or remove an introduction advisor, as existing proxies

from the factory will not show the interface change. (You can obtain a new proxy from the factory to

avoid this problem.)

A simple example of casting an AOP proxy to the Advised interface and examining and manipulating

its advice:

Advised advised = (Advised) myObject;

Advisor[] advisors = advised.getAdvisors();

int oldAdvisorCount = advisors.length;

System.out.println(oldAdvisorCount + " advisors");

// Add an advice like an interceptor without a pointcut

// Will match all proxied methods

// Can use for interceptors, before, after returning or throws advice

advised.addAdvice(new DebugInterceptor());

// Add selective advice using a pointcut

advised.addAdvisor(new DefaultPointcutAdvisor(mySpecialPointcut, myAdvice));

assertEquals("Added two advisors", oldAdvisorCount + 2, advised.getAdvisors().length);

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 260

Note

It’s questionable whether it’s advisable (no pun intended) to modify advice on a business object

in production, although there are no doubt legitimate usage cases. However, it can be very useful

in development: for example, in tests. I have sometimes found it very useful to be able to add test

code in the form of an interceptor or other advice, getting inside a method invocation I want to test.

(For example, the advice can get inside a transaction created for that method: for example, to run

SQL to check that a database was correctly updated, before marking the transaction for roll back.)

Depending on how you created the proxy, you can usually set a frozen flag, in which case the Advised

isFrozen() method will return true, and any attempts to modify advice through addition or removal

will result in an AopConfigException. The ability to freeze the state of an advised object is useful in

some cases, for example, to prevent calling code removing a security interceptor. It may also be used

in Spring 1.1 to allow aggressive optimization if runtime advice modification is known not to be required.

10.9 Using the "auto-proxy" facility

So far we’ve considered explicit creation of AOP proxies using a ProxyFactoryBean or similar factory

bean.

Spring also allows us to use "auto-proxy" bean definitions, which can automatically proxy selected bean

definitions. This is built on Spring "bean post processor" infrastructure, which enables modification of

any bean definition as the container loads.

In this model, you set up some special bean definitions in your XML bean definition file to configure the

auto proxy infrastructure. This allows you just to declare the targets eligible for auto-proxying: you don’t

need to use ProxyFactoryBean.

There are two ways to do this:

• Using an auto-proxy creator that refers to specific beans in the current context.

• A special case of auto-proxy creation that deserves to be considered separately; auto-proxy creation

driven by source-level metadata attributes.

Autoproxy bean definitions

The org.springframework.aop.framework.autoproxy package provides the following

standard auto-proxy creators.

BeanNameAutoProxyCreator

The BeanNameAutoProxyCreator class is a BeanPostProcessor that automatically creates AOP

proxies for beans with names matching literal values or wildcards.

<list>

<value>myInterceptor</value>

</list>

</property>

</bean>

As with ProxyFactoryBean, there is an interceptorNames property rather than a list of

interceptors, to allow correct behavior for prototype advisors. Named "interceptors" can be advisors or

any advice type.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 261

As with auto proxying in general, the main point of using BeanNameAutoProxyCreator is to apply the

same configuration consistently to multiple objects, with minimal volume of configuration. It is a popular

choice for applying declarative transactions to multiple objects.

Bean definitions whose names match, such as "jdkMyBean" and "onlyJdk" in the above example, are

plain old bean definitions with the target class. An AOP proxy will be created automatically by the

BeanNameAutoProxyCreator. The same advice will be applied to all matching beans. Note that if

advisors are used (rather than the interceptor in the above example), the pointcuts may apply differently

to different beans.

DefaultAdvisorAutoProxyCreator

A more general and extremely powerful auto proxy creator is DefaultAdvisorAutoProxyCreator.

This will automagically apply eligible advisors in the current context, without the need to include

specific bean names in the auto-proxy advisor’s bean definition. It offers the same merit of consistent

configuration and avoidance of duplication as BeanNameAutoProxyCreator.

Using this mechanism involves:

• Specifying a DefaultAdvisorAutoProxyCreator bean definition.

• Specifying any number of Advisors in the same or related contexts. Note that these must be Advisors,

not just interceptors or other advices. This is necessary because there must be a pointcut to evaluate,

to check the eligibility of each advice to candidate bean definitions.

The DefaultAdvisorAutoProxyCreator will automatically evaluate the pointcut contained in each

advisor, to see what (if any) advice it should apply to each business object (such as "businessObject1"

and "businessObject2" in the example).

This means that any number of advisors can be applied automatically to each business object. If no

pointcut in any of the advisors matches any method in a business object, the object will not be proxied.

As bean definitions are added for new business objects, they will automatically be proxied if necessary.

Autoproxying in general has the advantage of making it impossible for callers or dependencies to obtain

an un-advised object. Calling getBean("businessObject1") on this ApplicationContext will return an AOP

proxy, not the target business object. (The "inner bean" idiom shown earlier also offers this benefit.)

</bean>

</bean>

The DefaultAdvisorAutoProxyCreator is very useful if you want to apply the same advice

consistently to many business objects. Once the infrastructure definitions are in place, you can simply

add new business objects without including specific proxy configuration. You can also drop in additional

aspects very easily - for example, tracing or performance monitoring aspects - with minimal change to

configuration.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 262

The DefaultAdvisorAutoProxyCreator offers support for filtering (using a naming convention

so that only certain advisors are evaluated, allowing use of multiple, differently configured,

AdvisorAutoProxyCreators in the same factory) and ordering. Advisors can implement the

org.springframework.core.Ordered interface to ensure correct ordering if this is an issue. The

TransactionAttributeSourceAdvisor used in the above example has a configurable order value; the

default setting is unordered.

AbstractAdvisorAutoProxyCreator

This is the superclass of DefaultAdvisorAutoProxyCreator. You can create your own auto-proxy creators

by subclassing this class, in the unlikely event that advisor definitions offer insufficient customization to

the behavior of the framework DefaultAdvisorAutoProxyCreator.

Using metadata-driven auto-proxying

A particularly important type of auto-proxying is driven by metadata. This produces a similar

programming model to .NET ServicedComponents. Instead of defining metadata in XML descriptors,

configuration for transaction management and other enterprise services is held in source-level attributes.

In this case, you use the DefaultAdvisorAutoProxyCreator, in combination with Advisors that

understand metadata attributes. The metadata specifics are held in the pointcut part of the candidate

advisors, rather than in the auto-proxy creation class itself.

This is really a special case of the DefaultAdvisorAutoProxyCreator, but deserves consideration

on its own. (The metadata-aware code is in the pointcuts contained in the advisors, not the AOP

framework itself.)

The /attributes directory of the JPetStore sample application shows the use of attribute-

driven auto-proxying. In this case, there’s no need to use the TransactionProxyFactoryBean.

Simply defining transactional attributes on business objects is sufficient, because of the use

of metadata-aware pointcuts. The bean definitions include the following code, in /WEB-INF/

declarativeServices.xml. Note that this is generic, and can be used outside the JPetStore:

</bean>

<bean id="transactionInterceptor"

class="org.springframework.transaction.interceptor.TransactionInterceptor">

</bean>

</property>

</bean>

The DefaultAdvisorAutoProxyCreator bean definition (the name is not significant, hence it

can even be omitted) will pick up all eligible pointcuts in the current application context. In this

case, the "transactionAdvisor" bean definition, of type TransactionAttributeSourceAdvisor, will

apply to classes or methods carrying a transaction attribute. The TransactionAttributeSourceAdvisor

depends on a TransactionInterceptor, via constructor dependency. The example resolves this via

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 263

autowiring. The AttributesTransactionAttributeSource depends on an implementation of the

org.springframework.metadata.Attributes interface. In this fragment, the "attributes" bean

satisfies this, using the Jakarta Commons Attributes API to obtain attribute information. (The application

code must have been compiled using the Commons Attributes compilation task.)

The /annotation directory of the JPetStore sample application contains an analogous example for

auto-proxying driven by JDK 1.5+ annotations. The following configuration enables automatic detection

of Spring’s Transactional annotation, leading to implicit proxies for beans containing that annotation:

</bean>

<bean id="transactionInterceptor"

class="org.springframework.transaction.interceptor.TransactionInterceptor">

</property>

</bean>

The TransactionInterceptor defined here depends on a PlatformTransactionManager

definition, which is not included in this generic file (although it could be) because it will be specific to the

application’s transaction requirements (typically JTA, as in this example, or Hibernate, JDO or JDBC):

<bean id="transactionManager"

class="org.springframework.transaction.jta.JtaTransactionManager"/>

Tip

If you require only declarative transaction management, using these generic XML definitions will

result in Spring automatically proxying all classes or methods with transaction attributes. You

won’t need to work directly with AOP, and the programming model is similar to that of .NET

ServicedComponents.

This mechanism is extensible. It’s possible to do auto-proxying based on custom attributes. You need to:

• Define your custom attribute.

• Specify an Advisor with the necessary advice, including a pointcut that is triggered by the presence

of the custom attribute on a class or method. You may be able to use an existing advice, merely

implementing a static pointcut that picks up the custom attribute.

It’s possible for such advisors to be unique to each advised class (for example, mixins): they simply

need to be defined as prototype, rather than singleton, bean definitions. For example, the LockMixin

introduction interceptor from the Spring test suite, shown above, could be used in conjunction with a

generic DefaultIntroductionAdvisor:

<bean id="lockableAdvisor" class="org.springframework.aop.support.DefaultIntroductionAdvisor"

scope="prototype">

<constructor-arg ref="lockMixin"/>

</bean>

Note that both lockMixin and lockableAdvisor are defined as prototypes.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 264

10.10 Using TargetSources

Spring offers the concept of a TargetSource, expressed in the

org.springframework.aop.TargetSource interface. This interface is responsible for returning

the "target object" implementing the join point. The TargetSource implementation is asked for a target

instance each time the AOP proxy handles a method invocation.

Developers using Spring AOP don’t normally need to work directly with TargetSources, but this provides

a powerful means of supporting pooling, hot swappable and other sophisticated targets. For example, a

pooling TargetSource can return a different target instance for each invocation, using a pool to manage

instances.

If you do not specify a TargetSource, a default implementation is used that wraps a local object. The

same target is returned for each invocation (as you would expect).

Let’s look at the standard target sources provided with Spring, and how you can use them.

Tip

When using a custom target source, your target will usually need to be a prototype rather than a

singleton bean definition. This allows Spring to create a new target instance when required.

Hot swappable target sources

The org.springframework.aop.target.HotSwappableTargetSource exists to allow the

target of an AOP proxy to be switched while allowing callers to keep their references to it.

Changing the target source’s target takes effect immediately. The HotSwappableTargetSource is

threadsafe.

You can change the target via the swap() method on HotSwappableTargetSource as follows:

HotSwappableTargetSource swapper = (HotSwappableTargetSource) beanFactory.getBean("swapper");

Object oldTarget = swapper.swap(newTarget);

The XML definitions required look as follows:

<constructor-arg ref="initialTarget"/>

</bean>

</bean>

The above swap() call changes the target of the swappable bean. Clients who hold a reference to that

bean will be unaware of the change, but will immediately start hitting the new target.

Although this example doesn’t add any advice - and it’s not necessary to add advice to use a

TargetSource - of course any TargetSource can be used in conjunction with arbitrary advice.

Pooling target sources

Using a pooling target source provides a similar programming model to stateless session EJBs, in which

a pool of identical instances is maintained, with method invocations going to free objects in the pool.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 265

A crucial difference between Spring pooling and SLSB pooling is that Spring pooling can be applied to

any POJO. As with Spring in general, this service can be applied in a non-invasive way.

Spring provides out-of-the-box support for Jakarta Commons Pool 1.3, which provides

a fairly efficient pooling implementation. You’ll need the commons-pool Jar on

your application’s classpath to use this feature. It’s also possible to subclass

org.springframework.aop.target.AbstractPoolingTargetSource to support any other

pooling API.

Sample configuration is shown below:

<bean id="businessObjectTarget" class="com.mycompany.MyBusinessObject"

scope="prototype">

... properties omitted

</bean>

</bean>

</bean>

Note that the target object - "businessObjectTarget" in the example - must be a prototype. This allows

the PoolingTargetSource implementation to create new instances of the target to grow the pool

as necessary. See the javadocs of AbstractPoolingTargetSource and the concrete subclass you

wish to use for information about its properties: "maxSize" is the most basic, and always guaranteed

to be present.

In this case, "myInterceptor" is the name of an interceptor that would need to be defined in the same

IoC context. However, it isn’t necessary to specify interceptors to use pooling. If you want only pooling,

and no other advice, don’t set the interceptorNames property at all.

It’s possible to configure Spring so as to be able to cast any pooled object to the

org.springframework.aop.target.PoolingConfig interface, which exposes information

about the configuration and current size of the pool through an introduction. You’ll need to define an

advisor like this:

</bean>

This advisor is obtained by calling a convenience method on the AbstractPoolingTargetSource

class, hence the use of MethodInvokingFactoryBean. This advisor’s name ("poolConfigAdvisor" here)

must be in the list of interceptors names in the ProxyFactoryBean exposing the pooled object.

The cast will look as follows:

PoolingConfig conf = (PoolingConfig) beanFactory.getBean("businessObject");

System.out.println("Max pool size is " + conf.getMaxSize());

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 266

Note

Pooling stateless service objects is not usually necessary. We don’t believe it should be the default

choice, as most stateless objects are naturally thread safe, and instance pooling is problematic

if resources are cached.

Simpler pooling is available using auto-proxying. It’s possible to set the TargetSources used by any

auto-proxy creator.

Prototype target sources

Setting up a "prototype" target source is similar to a pooling TargetSource. In this case, a new instance

of the target will be created on every method invocation. Although the cost of creating a new object isn’t

high in a modern JVM, the cost of wiring up the new object (satisfying its IoC dependencies) may be

more expensive. Thus you shouldn’t use this approach without very good reason.

To do this, you could modify the poolTargetSource definition shown above as follows. (I’ve also

changed the name, for clarity.)

</bean>

There’s only one property: the name of the target bean. Inheritance is used in the TargetSource

implementations to ensure consistent naming. As with the pooling target source, the target bean must

be a prototype bean definition.

ThreadLocal target sources

ThreadLocal target sources are useful if you need an object to be created for each incoming request

(per thread that is). The concept of a ThreadLocal provide a JDK-wide facility to transparently store

resource alongside a thread. Setting up a ThreadLocalTargetSource is pretty much the same as

was explained for the other types of target source:

</bean>

Note

ThreadLocals come with serious issues (potentially resulting in memory leaks) when incorrectly

using them in a multi-threaded and multi-classloader environments. One should always consider

wrapping a threadlocal in some other class and never directly use the ThreadLocal itself (except

of course in the wrapper class). Also, one should always remember to correctly set and unset

(where the latter simply involved a call to ThreadLocal.set(null)) the resource local to the

thread. Unsetting should be done in any case since not unsetting it might result in problematic

behavior. Spring’s ThreadLocal support does this for you and should always be considered in

favor of using ThreadLocals without other proper handling code.

10.11 Defining new Advice types

Spring AOP is designed to be extensible. While the interception implementation strategy is presently

used internally, it is possible to support arbitrary advice types in addition to the out-of-the-box

interception around advice, before, throws advice and after returning advice.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 267

The org.springframework.aop.framework.adapter package is an SPI package allowing

support for new custom advice types to be added without changing the core framework. The only

constraint on a custom Advice type is that it must implement the org.aopalliance.aop.Advice

marker interface.

Please refer to the org.springframework.aop.framework.adapter javadocs for further

information.

10.12 Further resources

Please refer to the Spring sample applications for further examples of Spring AOP:

• The JPetStore’s default configuration illustrates the use of the TransactionProxyFactoryBean

for declarative transaction management.

• The /attributes directory of the JPetStore illustrates the use of attribute-driven declarative

transaction management.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 268

11. Testing

11.1 Introduction to Spring Testing

Testing is an integral part of enterprise software development. This chapter focuses on the value-add

of the IoC principle to unit testing and on the benefits of the Spring Framework’s support for integration

testing. (A thorough treatment of testing in the enterprise is beyond the scope of this reference manual.)

11.2 Unit Testing

Dependency Injection should make your code less dependent on the container than it would be with

traditional Java EE development. The POJOs that make up your application should be testable in JUnit

or TestNG tests, with objects simply instantiated using the new operator, without Spring or any other

container. You can use mock objects (in conjunction with other valuable testing techniques) to test your

code in isolation. If you follow the architecture recommendations for Spring, the resulting clean layering

and componentization of your codebase will facilitate easier unit testing. For example, you can test

service layer objects by stubbing or mocking DAO or Repository interfaces, without needing to access

persistent data while running unit tests.

True unit tests typically run extremely quickly, as there is no runtime infrastructure to set up. Emphasizing

true unit tests as part of your development methodology will boost your productivity. You may not need

this section of the testing chapter to help you write effective unit tests for your IoC-based applications.

For certain unit testing scenarios, however, the Spring Framework provides the following mock objects

and testing support classes.

Mock Objects

Environment

The org.springframework.mock.env package contains mock implementations of the

Environment and PropertySource abstractions (see the section called “Bean definition profiles” and

the section called “PropertySource Abstraction”). MockEnvironment and MockPropertySource are

useful for developing out-of-container tests for code that depends on environment-specific properties.

JNDI

The org.springframework.mock.jndi package contains an implementation of the JNDI SPI,

which you can use to set up a simple JNDI environment for test suites or stand-alone applications.

If, for example, JDBC DataSources get bound to the same JNDI names in test code as within a

Java EE container, you can reuse both application code and configuration in testing scenarios without

modification.

Servlet API

The org.springframework.mock.web package contains a comprehensive set of Servlet API mock

objects, targeted at usage with Spring’s Web MVC framework, which are useful for testing web contexts

and controllers. These mock objects are generally more convenient to use than dynamic mock objects

such as EasyMock or existing Servlet API mock objects such as MockObjects.

Portlet API

The org.springframework.mock.web.portlet package contains a set of Portlet API mock

objects, targeted at usage with Spring’s Portlet MVC framework.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 269

Unit Testing support Classes

General utilities

The org.springframework.test.util package contains ReflectionTestUtils, which is a

collection of reflection-based utility methods. Developers use these methods in unit and integration

testing scenarios in which they need to set a non- public field or invoke a non- public setter method

when testing application code involving, for example:

• ORM frameworks such as JPA and Hibernate that condone private or protected field access as

opposed to public setter methods for properties in a domain entity.

• Spring’s support for annotations such as @Autowired, @Inject, and @Resource, which provides

dependency injection for private or protected fields, setter methods, and configuration methods.

Spring MVC

The org.springframework.test.web package contains ModelAndViewAssert, which you can

use in combination with JUnit, TestNG, or any other testing framework for unit tests dealing with Spring

MVC ModelAndView objects.

Unit testing Spring MVC Controllers

To test your Spring MVC Controllers, use ModelAndViewAssert combined

with MockHttpServletRequest, MockHttpSession, and so on from the

org.springframework.mock.web package.

Note: As of Spring 4.0, the set of mocks in the org.springframework.mock.web package is

now based on the Servlet 3.0 API.

11.3 Integration Testing

Overview

It is important to be able to perform some integration testing without requiring deployment to your

application server or connecting to other enterprise infrastructure. This will enable you to test things

such as:

• The correct wiring of your Spring IoC container contexts.

• Data access using JDBC or an ORM tool. This would include such things as the correctness of SQL

statements, Hibernate queries, JPA entity mappings, etc.

The Spring Framework provides first-class support for integration testing in the spring-test

module. The name of the actual JAR file might include the release version and might also

be in the long org.springframework.test form, depending on where you get it from

(see the section on Dependency Management for an explanation). This library includes the

org.springframework.test package, which contains valuable classes for integration testing with

a Spring container. This testing does not rely on an application server or other deployment environment.

Such tests are slower to run than unit tests but much faster than the equivalent Selenium tests or remote

tests that rely on deployment to an application server.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 270

In Spring 2.5 and later, unit and integration testing support is provided in the form of the annotation-driven

Spring TestContext Framework. The TestContext framework is agnostic of the actual testing framework

in use, thus allowing instrumentation of tests in various environments including JUnit, TestNG, and so on.

Goals of Integration Testing

Spring’s integration testing support has the following primary goals:

• To manage Spring IoC container caching between test execution.

• To provide Dependency Injection of test fixture instances.

• To provide transaction management appropriate to integration testing.

• To supply Spring-specific base classes that assist developers in writing integration tests.

The next few sections describe each goal and provide links to implementation and configuration details.

Context management and caching

The Spring TestContext Framework provides consistent loading of Spring ApplicationContexts and

WebApplicationContexts as well as caching of those contexts. Support for the caching of loaded

contexts is important, because startup time can become an issue — not because of the overhead of

Spring itself, but because the objects instantiated by the Spring container take time to instantiate. For

example, a project with 50 to 100 Hibernate mapping files might take 10 to 20 seconds to load the

mapping files, and incurring that cost before running every test in every test fixture leads to slower

overall test runs that reduce developer productivity.

Test classes typically declare either an array of resource locations for XML configuration

metadata — often in the classpath — or an array of annotated classes that is used to configure the

application. These locations or classes are the same as or similar to those specified in web.xml or

other deployment configuration files.

By default, once loaded, the configured ApplicationContext is reused for each test. Thus the

setup cost is incurred only once per test suite, and subsequent test execution is much faster. In this

context, the term test suite means all tests run in the same JVM — for example, all tests run from an

Ant, Maven, or Gradle build for a given project or module. In the unlikely case that a test corrupts the

application context and requires reloading — for example, by modifying a bean definition or the state of

an application object — the TestContext framework can be configured to reload the configuration and

rebuild the application context before executing the next test.

See the section called “Context management” and the section called “Context caching” with the

TestContext framework.

Dependency Injection of test fixtures

When the TestContext framework loads your application context, it can optionally configure instances

of your test classes via Dependency Injection. This provides a convenient mechanism for setting up

test fixtures using preconfigured beans from your application context. A strong benefit here is that you

can reuse application contexts across various testing scenarios (e.g., for configuring Spring-managed

object graphs, transactional proxies, DataSources, etc.), thus avoiding the need to duplicate complex

test fixture setup for individual test cases.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 271

As an example, consider the scenario where we have a class, HibernateTitleRepository, that

implements data access logic for a Title domain entity. We want to write integration tests that test

the following areas:

• The Spring configuration: basically, is everything related to the configuration of the

HibernateTitleRepository bean correct and present?

• The Hibernate mapping file configuration: is everything mapped correctly, and are the correct lazy-

loading settings in place?

• The logic of the HibernateTitleRepository: does the configured instance of this class perform

as anticipated?

See dependency injection of test fixtures with the TestContext framework.

Transaction management

One common issue in tests that access a real database is their effect on the state of the persistence

store. Even when you’re using a development database, changes to the state may affect future tests.

Also, many operations — such as inserting or modifying persistent data — cannot be performed (or

verified) outside a transaction.

The TestContext framework addresses this issue. By default, the framework will create and roll back a

transaction for each test. You simply write code that can assume the existence of a transaction. If you

call transactionally proxied objects in your tests, they will behave correctly, according to their configured

transactional semantics. In addition, if a test method deletes the contents of selected tables while running

within the transaction managed for the test, the transaction will roll back by default, and the database

will return to its state prior to execution of the test. Transactional support is provided to a test via a

PlatformTransactionManager bean defined in the test’s application context.

If you want a transaction to commit — unusual, but occasionally useful when you want a particular

test to populate or modify the database — the TestContext framework can be instructed to cause the

transaction to commit instead of roll back via the @TransactionConfiguration and @Rollback

annotations.

See transaction management with the TestContext framework.

Support classes for integration testing

The Spring TestContext Framework provides several abstract support classes that simplify the writing

of integration tests. These base test classes provide well-defined hooks into the testing framework as

well as convenient instance variables and methods, which enable you to access:

• The ApplicationContext, for performing explicit bean lookups or testing the state of the context

as a whole.

• A JdbcTemplate, for executing SQL statements to query the database. Such queries can be used

to confirm database state both prior to and after execution of database-related application code, and

Spring ensures that such queries run in the scope of the same transaction as the application code.

When used in conjunction with an ORM tool, be sure to avoid false positives.

In addition, you may want to create your own custom, application-wide superclass with instance

variables and methods specific to your project.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 272

See support classes for the TestContext framework.

JDBC Testing Support

The org.springframework.test.jdbc package contains JdbcTestUtils, which is a collection

of JDBC related utility functions intended to simplify standard database testing scenarios. Specifically,

JdbcTestUtils provides the following static utility methods.

•countRowsInTable(..): counts the number of rows in the given table

•countRowsInTableWhere(..): counts the number of rows in the given table, using the provided

WHERE clause

•deleteFromTables(..): deletes all rows from the specified tables

•deleteFromTableWhere(..): deletes rows from the given table, using the provided WHERE clause

•dropTables(..): drops the specified tables

Note that AbstractTransactionalJUnit4SpringContextTests and

AbstractTransactionalTestNGSpringContextTests provide convenience methods which

delegate to the aforementioned methods in JdbcTestUtils.

The spring-jdbc module provides support for configuring and launching an embedded database

which can be used in integration tests that interact with a database. For details, see Section 14.8,

“Embedded database support” and the section called “Testing data access logic with an embedded

database”.

Annotations

Spring Testing Annotations

The Spring Framework provides the following set of Spring-specific annotations that you can use in your

unit and integration tests in conjunction with the TestContext framework. Refer to the corresponding

javadocs for further information, including default attribute values, attribute aliases, and so on.

•@ContextConfiguration

Defines class-level metadata that is used to determine how to load and configure an

ApplicationContext for integration tests. Specifically, @ContextConfiguration declares the

application context resource locations or the annotated classes that will be used to load the

context.

Resource locations are typically XML configuration files located in the classpath; whereas, annotated

classes are typically @Configuration classes. However, resource locations can also refer to files

in the file system, and annotated classes can be component classes, etc.

@ContextConfiguration("/test-config.xml")

public class XmlApplicationContextTests {

// class body...

}

@ContextConfiguration(classes = TestConfig.class)

public class ConfigClassApplicationContextTests {

// class body...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 273

As an alternative or in addition to declaring resource locations or annotated classes,

@ContextConfiguration may be used to declare ApplicationContextInitializer

classes.

@ContextConfiguration(initializers = CustomContextIntializer.class)

public class ContextInitializerTests {

// class body...

}

@ContextConfiguration may optionally be used to declare the ContextLoader strategy as well.

Note, however, that you typically do not need to explicitly configure the loader since the default loader

supports either resource locations or annotated classes as well as initializers.

@ContextConfiguration(locations = "/test-context.xml", loader = CustomContextLoader.class)

public class CustomLoaderXmlApplicationContextTests {

// class body...

}

Note

@ContextConfiguration provides support for inheriting resource locations or configuration

classes as well as context initializers declared by superclasses by default.

See the section called “Context management” and the @ContextConfiguration javadocs for

further details.

•@WebAppConfiguration

A class-level annotation that is used to declare that the ApplicationContext loaded

for an integration test should be a WebApplicationContext. The mere presence of

@WebAppConfiguration on a test class ensures that a WebApplicationContext will be loaded

for the test, using the default value of "file:src/main/webapp" for the path to the root of

the web application (i.e., the resource base path). The resource base path is used behind the

scenes to create a MockServletContext which serves as the ServletContext for the test’s

WebApplicationContext.

@ContextConfiguration

@WebAppConfiguration

public class WebAppTests {

// class body...

}

To override the default, specify a different base resource path via the implicit value attribute. Both

classpath: and file: resource prefixes are supported. If no resource prefix is supplied the path

is assumed to be a file system resource.

@ContextConfiguration

@WebAppConfiguration("classpath:test-web-resources")

public class WebAppTests {

// class body...

}

Note that @WebAppConfiguration must be used in conjunction with @ContextConfiguration,

either within a single test class or within a test class hierarchy. See the @WebAppConfiguration

javadocs for further details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 274

•@ContextHierarchy

A class-level annotation that is used to define a hierarchy of ApplicationContexts for

integration tests. @ContextHierarchy should be declared with a list of one or more

@ContextConfiguration instances, each of which defines a level in the context hierarchy. The

following examples demonstrate the use of @ContextHierarchy within a single test class; however,

@ContextHierarchy can also be used within a test class hierarchy.

@ContextHierarchy({

@ContextConfiguration("/parent-config.xml"),

@ContextConfiguration("/child-config.xml")

})

public class ContextHierarchyTests {

// class body...

}

@WebAppConfiguration

@ContextHierarchy({

@ContextConfiguration(classes = AppConfig.class),

@ContextConfiguration(classes = WebConfig.class)

})

public class WebIntegrationTests {

// class body...

}

If you need to merge or override the configuration for a given level of the context hierarchy within

a test class hierarchy, you must explicitly name that level by supplying the same value to the name

attribute in @ContextConfiguration at each corresponding level in the class hierarchy. See the

section called “Context hierarchies” and the @ContextHierarchy javadocs for further examples.

•@ActiveProfiles

A class-level annotation that is used to declare which bean definition profiles should be active when

loading an ApplicationContext for test classes.

@ContextConfiguration

@ActiveProfiles("dev")

public class DeveloperTests {

// class body...

}

@ContextConfiguration

@ActiveProfiles({"dev", "integration"})

public class DeveloperIntegrationTests {

// class body...

}

Note

@ActiveProfiles provides support for inheriting active bean definition profiles declared

by superclasses by default. It is also possible to resolve active bean definition profiles

programmatically by implementing a custom ActiveProfilesResolver and registering it

via the resolver attribute of @ActiveProfiles.

See the section called “Context configuration with environment profiles” and the @ActiveProfiles

javadocs for examples and further details.

•@TestPropertySource

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 275

A class-level annotation that is used to configure the locations of properties files and inlined properties

to be added to the Environment's set of PropertySources for an ApplicationContext loaded

for an integration test.

Test property sources have higher precedence than those loaded from the operating system’s

environment or Java system properties as well as property sources added by the application

declaratively via @PropertySource or programmatically. Thus, test property sources can be used

to selectively override properties defined in system and application property sources. Furthermore,

inlined properties have higher precedence than properties loaded from resource locations.

The following example demonstrates how to declare a properties file from the classpath.

@ContextConfiguration

@TestPropertySource("/test.properties")

public class MyIntegrationTests {

// class body...

}

The following example demonstrates how to declare inlined properties.

@ContextConfiguration

@TestPropertySource(properties = { "timezone = GMT", "port: 4242" })

public class MyIntegrationTests {

// class body...

}

•@DirtiesContext

Indicates that the underlying Spring ApplicationContext has been dirtied during the execution of

a test (i.e., modified or corrupted in some manner — for example, by changing the state of a singleton

bean) and should be closed, regardless of whether the test passed. When an application context is

marked dirty, it is removed from the testing framework’s cache and closed. As a consequence, the

underlying Spring container will be rebuilt for any subsequent test that requires a context with the

same configuration metadata.

@DirtiesContext can be used as both a class-level and method-level annotation within the same

test class. In such scenarios, the ApplicationContext is marked as dirty after any such annotated

method as well as after the entire class. If the ClassMode is set to AFTER_EACH_TEST_METHOD,

the context is marked dirty after each test method in the class.

The following examples explain when the context would be dirtied for various configuration scenarios:

• After the current test class, when declared on a class with class mode set to AFTER_CLASS (i.e.,

the default class mode).

@DirtiesContext

public class ContextDirtyingTests {

// some tests that result in the Spring container being dirtied

}

• After each test method in the current test class, when declared on a class with class mode set to

AFTER_EACH_TEST_METHOD.

@DirtiesContext(classMode = ClassMode.AFTER_EACH_TEST_METHOD)

public class ContextDirtyingTests {

// some tests that result in the Spring container being dirtied

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 276

• After the current test, when declared on a method.

@DirtiesContext

@Test

public void testProcessWhichDirtiesAppCtx() {

// some logic that results in the Spring container being dirtied

}

If @DirtiesContext is used in a test whose context is configured as part of a context hierarchy via

@ContextHierarchy, the hierarchyMode flag can be used to control how the context cache is

cleared. By default an exhaustive algorithm will be used that clears the context cache including not

only the current level but also all other context hierarchies that share an ancestor context common to

the current test; all ApplicationContexts that reside in a sub-hierarchy of the common ancestor

context will be removed from the context cache and closed. If the exhaustive algorithm is overkill for

a particular use case, the simpler current level algorithm can be specified instead, as seen below.

@ContextHierarchy({

@ContextConfiguration("/parent-config.xml"),

@ContextConfiguration("/child-config.xml")

})

public class BaseTests {

// class body...

}

public class ExtendedTests extends BaseTests {

@Test

@DirtiesContext(hierarchyMode = HierarchyMode.CURRENT_LEVEL)

public void test() {

// some logic that results in the child context being dirtied

}

For further details regarding the EXHAUSTIVE and CURRENT_LEVEL algorithms see the

DirtiesContext.HierarchyMode javadocs.

•@TestExecutionListeners

Defines class-level metadata for configuring which TestExecutionListeners should be registered

with the TestContextManager. Typically, @TestExecutionListeners is used in conjunction

with @ContextConfiguration.

@ContextConfiguration

@TestExecutionListeners({CustomTestExecutionListener.class, AnotherTestExecutionListener.class})

public class CustomTestExecutionListenerTests {

// class body...

}

@TestExecutionListeners supports inherited listeners by default. See the javadocs for an

example and further details.

•@TransactionConfiguration

Defines class-level metadata for configuring transactional tests. Specifically, the bean name of

the PlatformTransactionManager that should be used to drive transactions can be explicitly

specified if there are multiple beans of type PlatformTransactionManager in the test’s

ApplicationContext and if the bean name of the desired PlatformTransactionManager

is not "transactionManager". In addition, you can change the defaultRollback flag to false.

Typically, @TransactionConfiguration is used in conjunction with @ContextConfiguration.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 277

@ContextConfiguration

@TransactionConfiguration(transactionManager = "txMgr", defaultRollback = false)

public class CustomConfiguredTransactionalTests {

// class body...

}

Note

If the default conventions are sufficient for your test configuration, you can

avoid using @TransactionConfiguration altogether. In other words, if you have

only one transaction manager — or if you have multiple transaction managers but

the transaction manager for tests is named "transactionManager" or specified via

a TransactionManagementConfigurer — and if you want transactions to roll

back automatically, then there is no need to annotate your test class with

@TransactionConfiguration.

•@Rollback

Indicates whether the transaction for the annotated test method should be rolled back after the test

method has completed. If true, the transaction is rolled back; otherwise, the transaction is committed.

Use @Rollback to override the default rollback flag configured at the class level.

@Rollback(false)

@Test

public void testProcessWithoutRollback() {

// ...

}

•@BeforeTransaction

Indicates that the annotated public void method should be executed before a transaction is started

for test methods configured to run within a transaction via the @Transactional annotation.

@BeforeTransaction

public void beforeTransaction() {

// logic to be executed before a transaction is started

}

•@AfterTransaction

Indicates that the annotated public void method should be executed after a transaction has ended

for test methods configured to run within a transaction via the @Transactional annotation.

@AfterTransaction

public void afterTransaction() {

// logic to be executed after a transaction has ended

}

•@Sql

Used to annotate a test class or test method to configure SQL scripts to be executed against a given

database during integration tests.

@Test

@Sql({"/test-schema.sql", "/test-user-data.sql"})

public void userTest {

// execute code that relies on the test schema and test data

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 278

See the section called “Executing SQL scripts declaratively with @Sql” for further details.

•@SqlConfig

Defines metadata that is used to determine how to parse and execute SQL scripts configured via the

@Sql annotation.

@Test

@Sql(

scripts = "/test-user-data.sql",

config = @SqlConfig(commentPrefix = "`", separator = "@@")

)

public void userTest {

// execute code that relies on the test data

}

•@SqlGroup

A container annotation that aggregates several @Sql annotations. Can be used natively, declaring

several nested @Sql annotations. Can also be used in conjunction with Java 8’s support for repeatable

annotations, where @Sql can simply be declared several times on the same class or method, implicitly

generating this container annotation.

@Test

@SqlGroup({

@Sql(scripts = "/test-schema.sql", config = @SqlConfig(commentPrefix = "`")),

@Sql("/test-user-data.sql")

)}

public void userTest {

// execute code that uses the test schema and test data

}

Standard Annotation Support

The following annotations are supported with standard semantics for all configurations of the Spring

TestContext Framework. Note that these annotations are not specific to tests and can be used anywhere

in the Spring Framework.

•@Autowired

•@Qualifier

•@Resource (javax.annotation) if JSR-250 is present

•@Inject (javax.inject) if JSR-330 is present

•@Named (javax.inject) if JSR-330 is present

•@PersistenceContext (javax.persistence) if JPA is present

•@PersistenceUnit (javax.persistence) if JPA is present

•@Required

•@Transactional

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 279

JSR-250 Lifecycle Annotations

In the Spring TestContext Framework @PostConstruct and @PreDestroy may be used with

standard semantics on any application components configured in the ApplicationContext;

however, these lifecycle annotations have limited usage within an actual test class.

If a method within a test class is annotated with @PostConstruct, that method will be executed

before any before methods of the underlying test framework (e.g., methods annotated with JUnit’s

@Before), and that will apply for every test method in the test class. On the other hand, if a

method within a test class is annotated with @PreDestroy, that method will never be executed.

Within a test class it is therefore recommended to use test lifecycle callbacks from the underlying

test framework instead of @PostConstruct and @PreDestroy.

Spring JUnit Testing Annotations

The following annotations are only supported when used in conjunction with the

SpringJUnit4ClassRunner or the JUnit support classes.

•@IfProfileValue

Indicates that the annotated test is enabled for a specific testing environment. If the configured

ProfileValueSource returns a matching value for the provided name, the test is enabled. This

annotation can be applied to an entire class or to individual methods. Class-level usage overrides

method-level usage.

@IfProfileValue(name="java.vendor", value="Oracle Corporation")

@Test

public void testProcessWhichRunsOnlyOnOracleJvm() {

// some logic that should run only on Java VMs from Oracle Corporation

}

Alternatively, you can configure @IfProfileValue with a list of values (with OR semantics) to

achieve TestNG-like support for test groups in a JUnit environment. Consider the following example:

@IfProfileValue(name="test-groups", values={"unit-tests", "integration-tests"})

@Test

public void testProcessWhichRunsForUnitOrIntegrationTestGroups() {

// some logic that should run only for unit and integration test groups

}

•@ProfileValueSourceConfiguration

Class-level annotation that specifies what type of ProfileValueSource to

use when retrieving profile values configured through the @IfProfileValue

annotation. If @ProfileValueSourceConfiguration is not declared for a test,

SystemProfileValueSource is used by default.

@ProfileValueSourceConfiguration(CustomProfileValueSource.class)

public class CustomProfileValueSourceTests {

// class body...

}

•@Timed

Indicates that the annotated test method must finish execution in a specified time period (in

milliseconds). If the text execution time exceeds the specified time period, the test fails.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 280

The time period includes execution of the test method itself, any repetitions of the test (see @Repeat),

as well as any set up or tear down of the test fixture.

@Timed(millis=1000)

public void testProcessWithOneSecondTimeout() {

// some logic that should not take longer than 1 second to execute

}

Spring’s @Timed annotation has different semantics than JUnit’s @Test(timeout=...) support.

Specifically, due to the manner in which JUnit handles test execution timeouts (that is, by executing

the test method in a separate Thread), @Test(timeout=...) preemptively fails the test if the test

takes too long. Spring’s @Timed, on the other hand, does not preemptively fail the test but rather

waits for the test to complete before failing.

•@Repeat

Indicates that the annotated test method must be executed repeatedly. The number of times that the

test method is to be executed is specified in the annotation.

The scope of execution to be repeated includes execution of the test method itself as well as any set

up or tear down of the test fixture.

@Repeat(10)

@Test

public void testProcessRepeatedly() {

// ...

}

Meta-Annotation Support for Testing

As of Spring Framework 4.0, it is possible to use test-related annotations as meta-annotations in order

to create custom composed annotations and reduce configuration duplication across a test suite.

Each of the following may be used as meta-annotations in conjunction with the TestContext framework.

•@ContextConfiguration

•@ContextHierarchy

•@ActiveProfiles

•@TestPropertySource

•@DirtiesContext

•@WebAppConfiguration

•@TestExecutionListeners

•@Transactional

•@BeforeTransaction

•@AfterTransaction

•@TransactionConfiguration

•@Rollback

•@Sql

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 281

•@SqlConfig

•@SqlGroup

•@Repeat

•@Timed

•@IfProfileValue

•@ProfileValueSourceConfiguration

For example, if we discover that we are repeating the following configuration across our JUnit-based

test suite…

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"})

@ActiveProfiles("dev")

@Transactional

public class OrderRepositoryTests { }

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"})

@ActiveProfiles("dev")

@Transactional

public class UserRepositoryTests { }

We can reduce the above duplication by introducing a custom composed annotation that centralizes

the common test configuration like this:

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"})

@ActiveProfiles("dev")

@Transactional

public @interface TransactionalDevTest { }

Then we can use our custom @TransactionalDevTest annotation to simplify the configuration of

individual test classes as follows:

@RunWith(SpringJUnit4ClassRunner.class)

@TransactionalDevTest

public class OrderRepositoryTests { }

@RunWith(SpringJUnit4ClassRunner.class)

@TransactionalDevTest

public class UserRepositoryTests { }

Spring TestContext Framework

The Spring TestContext Framework (located in the org.springframework.test.context

package) provides generic, annotation-driven unit and integration testing support that is agnostic of

the testing framework in use. The TestContext framework also places a great deal of importance on

convention over configuration with reasonable defaults that can be overridden through annotation-based

configuration.

In addition to generic testing infrastructure, the TestContext framework provides explicit support for JUnit

and TestNG in the form of abstract support classes. For JUnit, Spring also provides a custom JUnit

Runner that allows one to write so-called POJO test classes. POJO test classes are not required to

extend a particular class hierarchy.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 282

The following section provides an overview of the internals of the TestContext framework. If you are

only interested in using the framework and not necessarily interested in extending it with your own

custom listeners or custom loaders, feel free to go directly to the configuration (context management,

dependency injection, transaction management), support classes, and annotation support sections.

Key abstractions

The core of the framework consists of the TestContext and TestContextManager classes

and the TestExecutionListener, ContextLoader, and SmartContextLoader interfaces. A

TestContextManager is created on a per-test basis (e.g., for the execution of a single test method

in JUnit). The TestContextManager in turn manages a TestContext that holds the context of

the current test. The TestContextManager also updates the state of the TestContext as the

test progresses and delegates to TestExecutionListeners, which instrument the actual test

execution by providing dependency injection, managing transactions, and so on. A ContextLoader

(or SmartContextLoader) is responsible for loading an ApplicationContext for a given test

class. Consult the javadocs and the Spring test suite for further information and examples of various

implementations.

•TestContext: Encapsulates the context in which a test is executed, agnostic of the actual

testing framework in use, and provides context management and caching support for the test

instance for which it is responsible. The TestContext also delegates to a ContextLoader (or

SmartContextLoader) to load an ApplicationContext if requested.

•TestContextManager: The main entry point into the Spring TestContext Framework, which

manages a single TestContext and signals events to all registered TestExecutionListeners

at well-defined test execution points:

• prior to any before class methods of a particular testing framework

• test instance preparation

• prior to any before methods of a particular testing framework

• after any after methods of a particular testing framework

• after any after class methods of a particular testing framework

•TestExecutionListener: Defines a listener API for reacting to test execution events published

by the TestContextManager with which the listener is registered. See the section called

“TestExecutionListener configuration”.

•ContextLoader: Strategy interface introduced in Spring 2.5 for loading an ApplicationContext

for an integration test managed by the Spring TestContext Framework.

Implement SmartContextLoader instead of this interface in order to provide support for

annotated classes, active bean definition profiles, test property sources, context hierarchies, and

WebApplicationContexts.

•SmartContextLoader: Extension of the ContextLoader interface introduced in Spring 3.1.

The SmartContextLoader SPI supersedes the ContextLoader SPI that was introduced in Spring

2.5. Specifically, a SmartContextLoader can choose to process resource locations, annotated

classes, or context initializers. Furthermore, a SmartContextLoader can set active bean

definition profiles and test property sources in the context that it loads.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 283

Spring provides the following implementations:

•DelegatingSmartContextLoader: one of two default loaders which delegates internally

to an AnnotationConfigContextLoader, a GenericXmlContextLoader, or a

GenericGroovyXmlContextLoader depending either on the configuration declared for the test

class or on the presence of default locations or default configuration classes. Groovy support is

only enabled if Groovy is on the classpath.

•WebDelegatingSmartContextLoader: one of two default loaders which delegates internally

to an AnnotationConfigWebContextLoader, a GenericXmlWebContextLoader, or a

GenericGroovyXmlWebContextLoader depending either on the configuration declared for

the test class or on the presence of default locations or default configuration classes. A web

ContextLoader will only be used if @WebAppConfiguration is present on the test class.

Groovy support is only enabled if Groovy is on the classpath.

•AnnotationConfigContextLoader: loads a standard ApplicationContext from annotated

classes.

•AnnotationConfigWebContextLoader: loads a WebApplicationContext from annotated

classes.

•GenericGroovyXmlContextLoader: loads a standard ApplicationContext from resource

locations that are either Groovy scripts or XML configuration files.

•GenericGroovyXmlWebContextLoader: loads a WebApplicationContext from resource

locations that are either Groovy scripts or XML configuration files.

•GenericXmlContextLoader: loads a standard ApplicationContext from XML resource

locations.

•GenericXmlWebContextLoader: loads a WebApplicationContext from XML resource

locations.

•GenericPropertiesContextLoader: loads a standard ApplicationContext from Java

Properties files.

The following sections explain how to configure the TestContext framework through annotations and

provide working examples of how to write unit and integration tests with the framework.

TestExecutionListener configuration

Spring provides the following TestExecutionListener implementations that are registered by

default, exactly in this order.

•ServletTestExecutionListener: configures Servlet API mocks for a

WebApplicationContext

•DependencyInjectionTestExecutionListener: provides dependency injection for the test

instance

•DirtiesContextTestExecutionListener: handles the @DirtiesContext annotation

•TransactionalTestExecutionListener: provides transactional test execution with default

rollback semantics

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 284

•SqlScriptsTestExecutionListener: executes SQL scripts configured via the @Sql annotation

Registering custom TestExecutionListeners

Custom TestExecutionListeners can be registered for a test class and its subclasses

via the @TestExecutionListeners annotation. See annotation support and the javadocs for

@TestExecutionListeners for details and examples.

Automatic discovery of default TestExecutionListeners

Registering custom TestExecutionListeners via @TestExecutionListeners is suitable for

custom listeners that are used in limited testing scenarios; however, it can become cumbersome if

a custom listener needs to be used across a test suite. To address this issue, Spring Framework

4.1 supports automatic discovery of default TestExecutionListener implementations via the

SpringFactoriesLoader mechanism.

Specifically, the spring-test module declares all core default TestExecutionListeners under

the org.springframework.test.context.TestExecutionListener key in its META-INF/

spring.factories properties file. Third-party frameworks and developers can contribute their own

TestExecutionListeners to the list of default listeners in the same manner via their own META-

INF/spring.factories properties file.

Ordering TestExecutionListeners

When the TestContext framework discovers default TestExecutionListeners via the

aforementioned SpringFactoriesLoader mechanism, the instantiated listeners are sorted

using Spring’s AnnotationAwareOrderComparator which honors Spring’s Ordered interface

and @Order annotation for ordering. AbstractTestExecutionListener and all default

TestExecutionListeners provided by Spring implement Ordered with appropriate values.

Third-party frameworks and developers should therefore make sure that their default

TestExecutionListeners are registered in the proper order by implementing Ordered or

declaring @Order. Consult the javadocs for the getOrder() methods of the core default

TestExecutionListeners for details on what values are assigned to each core listener.

Merging TestExecutionListeners

If a custom TestExecutionListener is registered via @TestExecutionListeners, the default

listeners will not be registered. In most common testing scenarios, this effectively forces the developer

to manually declare all default listeners in addition to any custom listeners. The following listing

demonstrates this style of configuration.

@ContextConfiguration

@TestExecutionListeners({

MyCustomTestExecutionListener.class,

ServletTestExecutionListener.class,

DependencyInjectionTestExecutionListener.class,

DirtiesContextTestExecutionListener.class,

TransactionalTestExecutionListener.class,

SqlScriptsTestExecutionListener.class

})

public class MyTest {

// class body...

}

The challenge with this approach is that it requires that the developer know exactly which

listeners are registered by default. Moreover, the set of default listeners can change from

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 285

release to release — for example, SqlScriptsTestExecutionListener was introduced in Spring

Framework 4.1. Furthermore, third-party frameworks like Spring Security register their own default

TestExecutionListeners via the aforementioned automatic discovery mechanism.

To avoid having to be aware of and re-declare all default listeners, the mergeMode

attribute of @TestExecutionListeners can be set to MergeMode.MERGE_WITH_DEFAULTS.

MERGE_WITH_DEFAULTS indicates that locally declared listeners should be merged with the default

listeners. The merging algorithm ensures that duplicates are removed from the list and that the resulting

set of merged listeners is sorted according to the semantics of AnnotationAwareOrderComparator

as described in the section called “Ordering TestExecutionListeners”. If a listener implements Ordered

or is annotated with @Order it can influence the position in which it is merged with the defaults;

otherwise, locally declared listeners will simply be appended to the list of default listeners when merged.

For example, if the MyCustomTestExecutionListener class in the previous example configures its

order value (for example, 500) to be less than the order of the ServletTestExecutionListener

(which happens to be 1000), the MyCustomTestExecutionListener can then be automatically

merged with the list of defaults in front of the ServletTestExecutionListener, and the previous

example could be replaced with the following.

@ContextConfiguration

@TestExecutionListeners(

listeners = MyCustomTestExecutionListener.class,

mergeMode = MERGE_WITH_DEFAULTS,

)

public class MyTest {

// class body...

}

Context management

Each TestContext provides context management and caching support for the test instance

it is responsible for. Test instances do not automatically receive access to the configured

ApplicationContext. However, if a test class implements the ApplicationContextAware

interface, a reference to the ApplicationContext is supplied to the test instance.

Note that AbstractJUnit4SpringContextTests and AbstractTestNGSpringContextTests

implement ApplicationContextAware and therefore provide access to the ApplicationContext

automatically.

@Autowired ApplicationContext

As an alternative to implementing the ApplicationContextAware interface, you can inject the

application context for your test class through the @Autowired annotation on either a field or

setter method. For example:

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration

public class MyTest {

@Autowired

private ApplicationContext applicationContext;

// class body...

}

Similarly, if your test is configured to load a WebApplicationContext, you can inject the web

application context into your test as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 286

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextConfiguration

public class MyWebAppTest {

@Autowired

private WebApplicationContext wac;

// class body...

}

Dependency injection via @Autowired is provided by the

DependencyInjectionTestExecutionListener which is configured by default (see the

section called “Dependency injection of test fixtures”).

Test classes that use the TestContext framework do not need to extend any particular class or implement

a specific interface to configure their application context. Instead, configuration is achieved simply

by declaring the @ContextConfiguration annotation at the class level. If your test class does

not explicitly declare application context resource locations or annotated classes, the configured

ContextLoader determines how to load a context from a default location or default configuration

classes. In addition to context resource locations and annotated classes, an application context

can also be configured via application context initializers.

The following sections explain how to configure an ApplicationContext via XML configuration

files, annotated classes (typically @Configuration classes), or context initializers using Spring’s

@ContextConfiguration annotation. Alternatively, you can implement and configure your own

custom SmartContextLoader for advanced use cases.

Context configuration with XML resources

To load an ApplicationContext for your tests using XML configuration files, annotate your test

class with @ContextConfiguration and configure the locations attribute with an array that

contains the resource locations of XML configuration metadata. A plain or relative path — for example

"context.xml"— will be treated as a classpath resource that is relative to the package in which the

test class is defined. A path starting with a slash is treated as an absolute classpath location, for example

"/org/example/config.xml". A path which represents a resource URL (i.e., a path prefixed with

classpath:, file:, http:, etc.) will be used as is.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from "/app-config.xml" and

// "/test-config.xml" in the root of the classpath

@ContextConfiguration(locations={"/app-config.xml", "/test-config.xml"})

public class MyTest {

// class body...

}

@ContextConfiguration supports an alias for the locations attribute through the standard Java

value attribute. Thus, if you do not need to declare additional attributes in @ContextConfiguration,

you can omit the declaration of the locations attribute name and declare the resource locations by

using the shorthand format demonstrated in the following example.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration({"/app-config.xml", "/test-config.xml"})

public class MyTest {

// class body...

}

If you omit both the locations and value attributes from the @ContextConfiguration

annotation, the TestContext framework will attempt to detect a default XML resource location.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 287

Specifically, GenericXmlContextLoader and GenericXmlWebContextLoader detect a default

location based on the name of the test class. If your class is named com.example.MyTest,

GenericXmlContextLoader loads your application context from "classpath:com/example/

MyTest-context.xml".

package com.example;

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from

// "classpath:com/example/MyTest-context.xml"

@ContextConfiguration

public class MyTest {

// class body...

}

Context configuration with Groovy scripts

To load an ApplicationContext for your tests using Groovy scripts that utilize the Groovy Bean

Definition DSL, annotate your test class with @ContextConfiguration and configure the locations

or value attribute with an array that contains the resource locations of Groovy scripts. Resource lookup

semantics for Groovy scripts are the same as those described for XML configuration files.

Enabling Groovy script support

Support for using Groovy scripts to load an ApplicationContext in the Spring TestContext

Framework is enabled automatically if Groovy is on the classpath.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from "/AppConfig.groovy" and

// "/TestConfig.groovy" in the root of the classpath

@ContextConfiguration({"/AppConfig.groovy", "/TestConfig.Groovy"})

public class MyTest {

// class body...

}

If you omit both the locations and value attributes from the @ContextConfiguration

annotation, the TestContext framework will attempt to detect a default Groovy script. Specifically,

GenericGroovyXmlContextLoader and GenericGroovyXmlWebContextLoader detect a

default location based on the name of the test class. If your class is named com.example.MyTest,

the Groovy context loader will load your application context from "classpath:com/example/

MyTestContext.groovy".

package com.example;

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from

// "classpath:com/example/MyTestContext.groovy"

@ContextConfiguration

public class MyTest {

// class body...

}

Declaring XML config and Groovy scripts simultaneously

Both XML configuration files and Groovy scripts can be declared simultaneously via the

locations or value attribute of @ContextConfiguration. If the path to a configured

resource location ends with .xml it will be loaded using an XmlBeanDefinitionReader;

otherwise it will be loaded using a GroovyBeanDefinitionReader.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 288

The following listing demonstrates how to combine both in an integration test.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from

// "/app-config.xml" and "/TestConfig.groovy"

@ContextConfiguration({ "/app-config.xml", "/TestConfig.groovy" })

public class MyTest {

// class body...

}

Context configuration with annotated classes

To load an ApplicationContext for your tests using annotated classes (see Section 5.12,

“Java-based container configuration”), annotate your test class with @ContextConfiguration and

configure the classes attribute with an array that contains references to annotated classes.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from AppConfig and TestConfig

@ContextConfiguration(classes = {AppConfig.class, TestConfig.class})

public class MyTest {

// class body...

}

Annotated Classes

The term annotated class can refer to any of the following.

• A class annotated with @Configuration

• A component (i.e., a class annotated with @Component, @Service, @Repository, etc.)

• A JSR-330 compliant class that is annotated with javax.inject annotations

• Any other class that contains @Bean-methods

Consult the javadocs of @Configuration and @Bean for further information regarding the

configuration and semantics of annotated classes, paying special attention to the discussion of

`@Bean` Lite Mode.

If you omit the classes attribute from the @ContextConfiguration annotation, the TestContext

framework will attempt to detect the presence of default configuration classes. Specifically,

AnnotationConfigContextLoader and AnnotationConfigWebContextLoader will detect all

static inner classes of the test class that meet the requirements for configuration class implementations

as specified in the @Configuration javadocs. In the following example, the OrderServiceTest

class declares a static inner configuration class named Config that will be automatically used to load

the ApplicationContext for the test class. Note that the name of the configuration class is arbitrary.

In addition, a test class can contain more than one static inner configuration class if desired.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 289

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from the

// static inner Config class

@ContextConfiguration

public class OrderServiceTest {

@Configuration

static class Config {

// this bean will be injected into the OrderServiceTest class

@Bean

public OrderService orderService() {

OrderService orderService = new OrderServiceImpl();

// set properties, etc.

return orderService;

}

@Autowired

private OrderService orderService;

@Test

public void testOrderService() {

// test the orderService

}

Mixing XML, Groovy scripts, and annotated classes

It may sometimes be desirable to mix XML configuration files, Groovy scripts, and annotated classes

(i.e., typically @Configuration classes) to configure an ApplicationContext for your tests.

For example, if you use XML configuration in production, you may decide that you want to use

@Configuration classes to configure specific Spring-managed components for your tests, or vice

versa.

Furthermore, some third-party frameworks (like Spring Boot) provide first-class support for loading an

ApplicationContext from different types of resources simultaneously (e.g., XML configuration files,

Groovy scripts, and @Configuration classes). The Spring Framework historically has not supported

this for standard deployments. Consequently, most of the SmartContextLoader implementations

that the Spring Framework delivers in the spring-test module support only one resource type per

test context; however, this does not mean that you cannot use both. One exception to the general

rule is that the GenericGroovyXmlContextLoader and GenericGroovyXmlWebContextLoader

support both XML configuration files and Groovy scripts simultaneously. Furthermore, third-

party frameworks may choose to support the declaration of both locations and classes via

@ContextConfiguration, and with the standard testing support in the TestContext framework, you

have the following options.

If you want to use resource locations (e.g., XML or Groovy) and @Configuration classes to configure

your tests, you will have to pick one as the entry point, and that one will have to include or import the

other. For example, in XML or Groovy scripts you can include @Configuration classes via component

scanning or define them as normal Spring beans; whereas, in a @Configuration class you can use

@ImportResource to import XML configuration files. Note that this behavior is semantically equivalent

to how you configure your application in production: in production configuration you will define either

a set of XML or Groovy resource locations or a set of @Configuration classes that your production

ApplicationContext will be loaded from, but you still have the freedom to include or import the other

type of configuration.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 290

Context configuration with context initializers

To configure an ApplicationContext for your tests using context initializers, annotate your test

class with @ContextConfiguration and configure the initializers attribute with an array that

contains references to classes that implement ApplicationContextInitializer. The declared

context initializers will then be used to initialize the ConfigurableApplicationContext that is

loaded for your tests. Note that the concrete ConfigurableApplicationContext type supported

by each declared initializer must be compatible with the type of ApplicationContext created by

the SmartContextLoader in use (i.e., typically a GenericApplicationContext). Furthermore,

the order in which the initializers are invoked depends on whether they implement Spring’s Ordered

interface, are annotated with Spring’s @Order or the standard @Priority annotation.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from TestConfig

// and initialized by TestAppCtxInitializer

@ContextConfiguration(

classes = TestConfig.class,

initializers = TestAppCtxInitializer.class)

public class MyTest {

// class body...

}

It is also possible to omit the declaration of XML configuration files or annotated classes in

@ContextConfiguration entirely and instead declare only ApplicationContextInitializer

classes which are then responsible for registering beans in the context — for example, by

programmatically loading bean definitions from XML files or configuration classes.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be initialized by EntireAppInitializer

// which presumably registers beans in the context

@ContextConfiguration(initializers = EntireAppInitializer.class)

public class MyTest {

// class body...

}

Context configuration inheritance

@ContextConfiguration supports boolean inheritLocations and inheritInitializers

attributes that denote whether resource locations or annotated classes and context initializers declared

by superclasses should be inherited. The default value for both flags is true. This means that a test

class inherits the resource locations or annotated classes as well as the context initializers declared by

any superclasses. Specifically, the resource locations or annotated classes for a test class are appended

to the list of resource locations or annotated classes declared by superclasses. Similarly, the initializers

for a given test class will be added to the set of initializers defined by test superclasses. Thus, subclasses

have the option of extending the resource locations, annotated classes, or context initializers.

If @ContextConfiguration's inheritLocations or inheritInitializers attribute is set to

false, the resource locations or annotated classes and the context initializers, respectively, for the test

class shadow and effectively replace the configuration defined by superclasses.

In the following example that uses XML resource locations, the ApplicationContext for

ExtendedTest will be loaded from "base-config.xml" and "extended-config.xml", in that order.

Beans defined in "extended-config.xml" may therefore override (i.e., replace) those defined in "base-

config.xml".

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 291

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from "/base-config.xml"

// in the root of the classpath

@ContextConfiguration("/base-config.xml")

public class BaseTest {

// class body...

}

// ApplicationContext will be loaded from "/base-config.xml" and

// "/extended-config.xml" in the root of the classpath

@ContextConfiguration("/extended-config.xml")

public class ExtendedTest extends BaseTest {

// class body...

}

Similarly, in the following example that uses annotated classes, the ApplicationContext for

ExtendedTest will be loaded from the BaseConfig and ExtendedConfig classes, in that

order. Beans defined in ExtendedConfig may therefore override (i.e., replace) those defined in

BaseConfig.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from BaseConfig

@ContextConfiguration(classes = BaseConfig.class)

public class BaseTest {

// class body...

}

// ApplicationContext will be loaded from BaseConfig and ExtendedConfig

@ContextConfiguration(classes = ExtendedConfig.class)

public class ExtendedTest extends BaseTest {

// class body...

}

In the following example that uses context initializers, the ApplicationContext for ExtendedTest

will be initialized using BaseInitializer and ExtendedInitializer. Note, however, that the

order in which the initializers are invoked depends on whether they implement Spring’s Ordered

interface, are annotated with Spring’s @Order or the standard @Priority annotation.

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be initialized by BaseInitializer

@ContextConfiguration(initializers = BaseInitializer.class)

public class BaseTest {

// class body...

}

// ApplicationContext will be initialized by BaseInitializer

// and ExtendedInitializer

@ContextConfiguration(initializers = ExtendedInitializer.class)

public class ExtendedTest extends BaseTest {

// class body...

}

Context configuration with environment profiles

Spring 3.1 introduced first-class support in the framework for the notion of environments and profiles

(a.k.a., bean definition profiles), and integration tests can be configured to activate particular bean

definition profiles for various testing scenarios. This is achieved by annotating a test class with the

@ActiveProfiles annotation and supplying a list of profiles that should be activated when loading

the ApplicationContext for the test.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 292

Note

@ActiveProfiles may be used with any implementation of the new SmartContextLoader

SPI, but @ActiveProfiles is not supported with implementations of the older ContextLoader

SPI.

Let’s take a look at some examples with XML configuration and @Configuration classes.

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:jdbc="http://www.springframework.org/schema/jdbc"

xmlns:jee="http://www.springframework.org/schema/jee"

xsi:schemaLocation="...">

<bean id="transferService"

class="com.bank.service.internal.DefaultTransferService">

<constructor-arg ref="accountRepository"/>

<constructor-arg ref="feePolicy"/>

</bean>

<bean id="accountRepository"

class="com.bank.repository.internal.JdbcAccountRepository">

<constructor-arg ref="dataSource"/>

</bean>

<bean id="feePolicy"

class="com.bank.service.internal.ZeroFeePolicy"/>

<jdbc:embedded-database id="dataSource">

<jdbc:script

location="classpath:com/bank/config/sql/schema.sql"/>

<jdbc:script

location="classpath:com/bank/config/sql/test-data.sql"/>

</jdbc:embedded-database>

</beans>

<jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/>

</beans>

<jdbc:embedded-database id="dataSource">

<jdbc:script

location="classpath:com/bank/config/sql/schema.sql"/>

</jdbc:embedded-database>

</beans>

package com.bank.service;

@RunWith(SpringJUnit4ClassRunner.class)

// ApplicationContext will be loaded from "classpath:/app-config.xml"

@ContextConfiguration("/app-config.xml")

@ActiveProfiles("dev")

public class TransferServiceTest {

@Autowired

private TransferService transferService;

@Test

public void testTransferService() {

// test the transferService

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 293

When TransferServiceTest is run, its ApplicationContext will be loaded from the app-

config.xml configuration file in the root of the classpath. If you inspect app-config.xml you’ll

notice that the accountRepository bean has a dependency on a dataSource bean; however,

dataSource is not defined as a top-level bean. Instead, dataSource is defined three times: in the

production profile, the dev profile, and the default profile.

By annotating TransferServiceTest with @ActiveProfiles("dev") we instruct the Spring

TestContext Framework to load the ApplicationContext with the active profiles set to {"dev"}.

As a result, an embedded database will be created and populated with test data, and the

accountRepository bean will be wired with a reference to the development DataSource. And that’s

likely what we want in an integration test.

It is sometimes useful to assign beans to a default profile. Beans within the default profile are only

included when no other profile is specifically activated. This can be used to define fallback beans to be

used in the application’s default state. For example, you may explicitly provide a data source for dev and

production profiles, but define an in-memory data source as a default when neither of these is active.

The following code listings demonstrate how to implement the same configuration and integration test

but using @Configuration classes instead of XML.

@Configuration

@Profile("dev")

public class StandaloneDataConfig {

@Bean

public DataSource dataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("classpath:com/bank/config/sql/schema.sql")

.addScript("classpath:com/bank/config/sql/test-data.sql")

.build();

}

@Configuration

@Profile("production")

public class JndiDataConfig {

@Bean

public DataSource dataSource() throws Exception {

Context ctx = new InitialContext();

return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");

}

@Configuration

@Profile("default")

public class DefaultDataConfig {

@Bean

public DataSource dataSource() {

return new EmbeddedDatabaseBuilder()

.setType(EmbeddedDatabaseType.HSQL)

.addScript("classpath:com/bank/config/sql/schema.sql")

.build();

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 294

@Configuration

public class TransferServiceConfig {

@Autowired DataSource dataSource;

@Bean

public TransferService transferService() {

return new DefaultTransferService(accountRepository(), feePolicy());

}

@Bean

public AccountRepository accountRepository() {

return new JdbcAccountRepository(dataSource);

}

@Bean

public FeePolicy feePolicy() {

return new ZeroFeePolicy();

}

package com.bank.service;

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(classes = {

TransferServiceConfig.class,

StandaloneDataConfig.class,

JndiDataConfig.class,

DefaultDataConfig.class})

@ActiveProfiles("dev")

public class TransferServiceTest {

@Autowired

private TransferService transferService;

@Test

public void testTransferService() {

// test the transferService

}

In this variation, we have split the XML configuration into four independent @Configuration classes:

•TransferServiceConfig: acquires a dataSource via dependency injection using @Autowired

•StandaloneDataConfig: defines a dataSource for an embedded database suitable for developer

tests

•JndiDataConfig: defines a dataSource that is retrieved from JNDI in a production environment

•DefaultDataConfig: defines a dataSource for a default embedded database in case no profile

is active

As with the XML-based configuration example, we still annotate TransferServiceTest with

@ActiveProfiles("dev"), but this time we specify all four configuration classes via the

@ContextConfiguration annotation. The body of the test class itself remains completely

unchanged.

It is often the case that a single set of profiles is used across multiple test classes within a given

project. Thus, to avoid duplicate declarations of the @ActiveProfiles annotation it is possible

to declare @ActiveProfiles once on a base class, and subclasses will automatically inherit the

@ActiveProfiles configuration from the base class. In the following example, the declaration

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 295

of @ActiveProfiles (as well as other annotations) has been moved to an abstract superclass,

AbstractIntegrationTest.

package com.bank.service;

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(classes = {

TransferServiceConfig.class,

StandaloneDataConfig.class,

JndiDataConfig.class,

DefaultDataConfig.class})

@ActiveProfiles("dev")

public abstract class AbstractIntegrationTest {

}

package com.bank.service;

// "dev" profile inherited from superclass

public class TransferServiceTest extends AbstractIntegrationTest {

@Autowired

private TransferService transferService;

@Test

public void testTransferService() {

// test the transferService

}

@ActiveProfiles also supports an inheritProfiles attribute that can be used to disable the

inheritance of active profiles.

package com.bank.service;

// "dev" profile overridden with "production"

@ActiveProfiles(profiles = "production", inheritProfiles = false)

public class ProductionTransferServiceTest extends AbstractIntegrationTest {

// test body

}

Furthermore, it is sometimes necessary to resolve active profiles for tests programmatically instead of

declaratively — for example, based on:

• the current operating system

• whether tests are being executed on a continuous integration build server

• the presence of certain environment variables

• the presence of custom class-level annotations

• etc.

To resolve active bean definition profiles programmatically, simply implement a custom

ActiveProfilesResolver and register it via the resolver attribute of @ActiveProfiles.

The following example demonstrates how to implement and register a custom

OperatingSystemActiveProfilesResolver. For further information, refer to the corresponding

javadocs.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 296

package com.bank.service;

// "dev" profile overridden programmatically via a custom resolver

@ActiveProfiles(

resolver = OperatingSystemActiveProfilesResolver.class,

inheritProfiles = false)

public class TransferServiceTest extends AbstractIntegrationTest {

// test body

}

package com.bank.service.test;

public class OperatingSystemActiveProfilesResolver implements ActiveProfilesResolver {

@Override

String[] resolve(Class<?> testClass) {

String profile = ...;

// determine the value of profile based on the operating system

return new String[] {profile};

}

Context configuration with test property sources

Spring 3.1 introduced first-class support in the framework for the notion of an environment with a

hierarchy of property sources, and since Spring 4.1 integration tests can be configured with test-

specific property sources. In contrast to the @PropertySource annotation used on @Configuration

classes, the @TestPropertySource annotation can be declared on a test class to declare resource

locations for test properties files or inlined properties. These test property sources will be added to the

Environment's set of PropertySources for the ApplicationContext loaded for the annotated

integration test.

Note

@TestPropertySource may be used with any implementation of the SmartContextLoader

SPI, but @TestPropertySource is not supported with implementations of the older

ContextLoader SPI.

Implementations of SmartContextLoader gain access to merged test property source

values via the getPropertySourceLocations() and getPropertySourceProperties()

methods in MergedContextConfiguration.

Declaring test property sources

Test properties files can be configured via the locations or value attribute of

@TestPropertySource as shown in the following example.

Both traditional and XML-based properties file formats are supported — for example, "classpath:/

com/example/test.properties" or "file:/path/to/file.xml".

Each path will be interpreted as a Spring Resource. A plain path — for example,

"test.properties"— will be treated as a classpath resource that is relative to the package in which

the test class is defined. A path starting with a slash will be treated as an absolute classpath resource,

for example: "/org/example/test.xml". A path which references a URL (e.g., a path prefixed

with classpath:, file:, http:, etc.) will be loaded using the specified resource protocol. Resource

location wildcards (e.g. **/*.properties) are not permitted: each location must evaluate to exactly

one .properties or .xml resource.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 297

@ContextConfiguration

@TestPropertySource("/test.properties")

public class MyIntegrationTests {

// class body...

}

Inlined properties in the form of key-value pairs can be configured via the properties attribute of

@TestPropertySource as shown in the following example. All key-value pairs will be added to the

enclosing Environment as a single test PropertySource with the highest precedence.

The supported syntax for key-value pairs is the same as the syntax defined for entries in a Java

properties file:

•"key=value"

•"key:value"

•"key value"

@ContextConfiguration

@TestPropertySource(properties = {"timezone = GMT", "port: 4242"})

public class MyIntegrationTests {

// class body...

}

Default properties file detection

If @TestPropertySource is declared as an empty annotation (i.e., without explicit values for the

locations or properties attributes), an attempt will be made to detect a default properties

file relative to the class that declared the annotation. For example, if the annotated test class is

com.example.MyTest, the corresponding default properties file is "classpath:com/example/

MyTest.properties". If the default cannot be detected, an IllegalStateException will be

thrown.

Precedence

Test property sources have higher precedence than those loaded from the operating system’s

environment or Java system properties as well as property sources added by the application

declaratively via @PropertySource or programmatically. Thus, test property sources can be used to

selectively override properties defined in system and application property sources. Furthermore, inlined

properties have higher precedence than properties loaded from resource locations.

In the following example, the timezone and port properties as well as any properties defined in "/

test.properties" will override any properties of the same name that are defined in system and

application property sources. Furthermore, if the "/test.properties" file defines entries for the

timezone and port properties those will be overridden by the inlined properties declared via the

properties attribute.

@ContextConfiguration

@TestPropertySource(

locations = "/test.properties",

properties = {"timezone = GMT", "port: 4242"}

)

public class MyIntegrationTests {

// class body...

}

Inheriting and overriding test property sources

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 298

@TestPropertySource supports boolean inheritLocations and inheritProperties

attributes that denote whether resource locations for properties files and inlined properties declared by

superclasses should be inherited. The default value for both flags is true. This means that a test class

inherits the locations and inlined properties declared by any superclasses. Specifically, the locations

and inlined properties for a test class are appended to the locations and inlined properties declared by

superclasses. Thus, subclasses have the option of extending the locations and inlined properties. Note

that properties that appear later will shadow (i.e.., override) properties of the same name that appear

earlier. In addition, the aforementioned precedence rules apply for inherited test property sources as

well.

If @TestPropertySource's inheritLocations or inheritProperties attribute is set to false,

the locations or inlined properties, respectively, for the test class shadow and effectively replace the

configuration defined by superclasses.

In the following example, the ApplicationContext for BaseTest will be loaded using only the

"base.properties" file as a test property source. In contrast, the ApplicationContext for

ExtendedTest will be loaded using the "base.properties" and "extended.properties" files

as test property source locations.

@TestPropertySource("base.properties")

@ContextConfiguration

public class BaseTest {

// ...

}

@TestPropertySource("extended.properties")

@ContextConfiguration

public class ExtendedTest extends BaseTest {

// ...

}

In the following example, the ApplicationContext for BaseTest will be loaded using only the inlined

key1 property. In contrast, the ApplicationContext for ExtendedTest will be loaded using the

inlined key1 and key2 properties.

@TestPropertySource(properties = "key1 = value1")

@ContextConfiguration

public class BaseTest {

// ...

}

@TestPropertySource(properties = "key2 = value2")

@ContextConfiguration

public class ExtendedTest extends BaseTest {

// ...

}

Loading a WebApplicationContext

Spring 3.2 introduced support for loading a WebApplicationContext in integration tests. To

instruct the TestContext framework to load a WebApplicationContext instead of a standard

ApplicationContext, simply annotate the respective test class with @WebAppConfiguration.

The presence of @WebAppConfiguration on your test class instructs the TestContext framework

(TCF) that a WebApplicationContext (WAC) should be loaded for your integration tests. In the

background the TCF makes sure that a MockServletContext is created and supplied to your test’s

WAC. By default the base resource path for your MockServletContext will be set to "src/main/

webapp". This is interpreted as a path relative to the root of your JVM (i.e., normally the path to

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 299

your project). If you’re familiar with the directory structure of a web application in a Maven project,

you’ll know that "src/main/webapp" is the default location for the root of your WAR. If you need to

override this default, simply provide an alternate path to the @WebAppConfiguration annotation (e.g.,

@WebAppConfiguration("src/test/webapp")). If you wish to reference a base resource path

from the classpath instead of the file system, just use Spring’s classpath: prefix.

Please note that Spring’s testing support for WebApplicationContexts is on par with its support for

standard ApplicationContexts. When testing with a WebApplicationContext you are free to

declare either XML configuration files or @Configuration classes via @ContextConfiguration.

You are of course also free to use any other test annotations such as @TestExecutionListeners,

@TransactionConfiguration, @ActiveProfiles, etc.

The following examples demonstrate some of the various configuration options for loading a

WebApplicationContext.

Conventions.

@RunWith(SpringJUnit4ClassRunner.class)

// defaults to "file:src/main/webapp"

@WebAppConfiguration

// detects "WacTests-context.xml" in same package

// or static nested @Configuration class

@ContextConfiguration

public class WacTests {

//...

}

The above example demonstrates the TestContext framework’s support for convention over

configuration. If you annotate a test class with @WebAppConfiguration without specifying a

resource base path, the resource path will effectively default to "file:src/main/webapp". Similarly, if

you declare @ContextConfiguration without specifying resource locations, annotated classes,

or context initializers, Spring will attempt to detect the presence of your configuration using

conventions (i.e., "WacTests-context.xml" in the same package as the WacTests class or static nested

@Configuration classes).

Default resource semantics.

@RunWith(SpringJUnit4ClassRunner.class)

// file system resource

@WebAppConfiguration("webapp")

// classpath resource

@ContextConfiguration("/spring/test-servlet-config.xml")

public class WacTests {

//...

}

This example demonstrates how to explicitly declare a resource base path with

@WebAppConfiguration and an XML resource location with @ContextConfiguration.

The important thing to note here is the different semantics for paths with these two

annotations. By default, @WebAppConfiguration resource paths are file system based; whereas,

@ContextConfiguration resource locations are classpath based.

Explicit resource semantics.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 300

@RunWith(SpringJUnit4ClassRunner.class)

// classpath resource

@WebAppConfiguration("classpath:test-web-resources")

// file system resource

@ContextConfiguration("file:src/main/webapp/WEB-INF/servlet-config.xml")

public class WacTests {

//...

}

In this third example, we see that we can override the default resource semantics for both annotations by

specifying a Spring resource prefix. Contrast the comments in this example with the previous example.

To provide comprehensive web testing support, Spring 3.2 introduced a

ServletTestExecutionListener that is enabled by default. When testing against a

WebApplicationContext this TestExecutionListener sets up default thread-local state

via Spring Web’s RequestContextHolder before each test method and creates

a MockHttpServletRequest, MockHttpServletResponse, and ServletWebRequest

based on the base resource path configured via @WebAppConfiguration.

ServletTestExecutionListener also ensures that the MockHttpServletResponse and

ServletWebRequest can be injected into the test instance, and once the test is complete it cleans

up thread-local state.

Once you have a WebApplicationContext loaded for your test you might find that you need to

interact with the web mocks — for example, to set up your test fixture or to perform assertions after

invoking your web component. The following example demonstrates which mocks can be autowired

into your test instance. Note that the WebApplicationContext and MockServletContext are

both cached across the test suite; whereas, the other mocks are managed per test method by the

ServletTestExecutionListener.

Injecting mocks.

@WebAppConfiguration

@ContextConfiguration

public class WacTests {

@Autowired

WebApplicationContext wac; // cached

@Autowired

MockServletContext servletContext; // cached

@Autowired

MockHttpSession session;

@Autowired

MockHttpServletRequest request;

@Autowired

MockHttpServletResponse response;

@Autowired

ServletWebRequest webRequest;

//...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 301

Context caching

Once the TestContext framework loads an ApplicationContext (or WebApplicationContext)

for a test, that context will be cached and reused for all subsequent tests that declare the same unique

context configuration within the same test suite. To understand how caching works, it is important to

understand what is meant by unique and test suite.

An ApplicationContext can be uniquely identified by the combination of configuration parameters

that are used to load it. Consequently, the unique combination of configuration parameters are used

to generate a key under which the context is cached. The TestContext framework uses the following

configuration parameters to build the context cache key:

•locations (from @ContextConfiguration)

•classes (from @ContextConfiguration)

•contextInitializerClasses (from @ContextConfiguration)

•contextLoader (from @ContextConfiguration)

•parent (from @ContextHierarchy)

•activeProfiles (from @ActiveProfiles)

•propertySourceLocations (from @TestPropertySource)

•propertySourceProperties (from @TestPropertySource)

•resourceBasePath (from @WebAppConfiguration)

For example, if TestClassA specifies {"app-config.xml", "test-config.xml"} for the

locations (or value) attribute of @ContextConfiguration, the TestContext framework will load

the corresponding ApplicationContext and store it in a static context cache under a key

that is based solely on those locations. So if TestClassB also defines {"app-config.xml",

"test-config.xml"} for its locations (either explicitly or implicitly through inheritance) but does

not define @WebAppConfiguration, a different ContextLoader, different active profiles, different

context initializers, different test property sources, or a different parent context, then the same

ApplicationContext will be shared by both test classes. This means that the setup cost for loading

an application context is incurred only once (per test suite), and subsequent test execution is much

faster.

Test suites and forked processes

The Spring TestContext framework stores application contexts in a static cache. This means that

the context is literally stored in a static variable. In other words, if tests execute in separate

processes the static cache will be cleared between each test execution, and this will effectively

disable the caching mechanism.

To benefit from the caching mechanism, all tests must run within the same process or test suite.

This can be achieved by executing all tests as a group within an IDE. Similarly, when executing

tests with a build framework such as Ant, Maven, or Gradle it is important to make sure that

the build framework does not fork between tests. For example, if the forkMode for the Maven

Surefire plug-in is set to always or pertest, the TestContext framework will not be able to cache

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 302

application contexts between test classes and the build process will run significantly slower as

a result.

In the unlikely case that a test corrupts the application context and requires reloading — for example, by

modifying a bean definition or the state of an application object — you can annotate your test class or

test method with @DirtiesContext (see the discussion of @DirtiesContext in the section called

“Spring Testing Annotations”). This instructs Spring to remove the context from the cache and rebuild

the application context before executing the next test. Note that support for the @DirtiesContext

annotation is provided by the DirtiesContextTestExecutionListener which is enabled by

default.

Context hierarchies

When writing integration tests that rely on a loaded Spring ApplicationContext, it is often

sufficient to test against a single context; however, there are times when it is beneficial or even

necessary to test against a hierarchy of ApplicationContexts. For example, if you are developing

a Spring MVC web application you will typically have a root WebApplicationContext loaded via

Spring’s ContextLoaderListener and a child WebApplicationContext loaded via Spring’s

DispatcherServlet. This results in a parent-child context hierarchy where shared components and

infrastructure configuration are declared in the root context and consumed in the child context by web-

specific components. Another use case can be found in Spring Batch applications where you often have

a parent context that provides configuration for shared batch infrastructure and a child context for the

configuration of a specific batch job.

As of Spring Framework 3.2.2, it is possible to write integration tests that use context hierarchies by

declaring context configuration via the @ContextHierarchy annotation, either on an individual test

class or within a test class hierarchy. If a context hierarchy is declared on multiple classes within a

test class hierarchy it is also possible to merge or override the context configuration for a specific,

named level in the context hierarchy. When merging configuration for a given level in the hierarchy

the configuration resource type (i.e., XML configuration files or annotated classes) must be consistent;

otherwise, it is perfectly acceptable to have different levels in a context hierarchy configured using

different resource types.

The following JUnit-based examples demonstrate common configuration scenarios for integration tests

that require the use of context hierarchies.

ControllerIntegrationTests represents a typical integration testing scenario for a Spring

MVC web application by declaring a context hierarchy consisting of two levels, one for the root

WebApplicationContext (loaded using the TestAppConfig @Configuration class) and one for

the dispatcher servlet WebApplicationContext (loaded using the WebConfig @Configuration

class). The WebApplicationContext that is autowired into the test instance is the one for the child

context (i.e., the lowest context in the hierarchy).

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextHierarchy({

@ContextConfiguration(classes = TestAppConfig.class),

@ContextConfiguration(classes = WebConfig.class)

})

public class ControllerIntegrationTests {

@Autowired

private WebApplicationContext wac;

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 303

The following test classes define a context hierarchy within a test class hierarchy. AbstractWebTests

declares the configuration for a root WebApplicationContext in a Spring-powered web

application. Note, however, that AbstractWebTests does not declare @ContextHierarchy;

consequently, subclasses of AbstractWebTests can optionally participate in a context hierarchy

or simply follow the standard semantics for @ContextConfiguration. SoapWebServiceTests

and RestWebServiceTests both extend AbstractWebTests and define a context hierarchy

via @ContextHierarchy. The result is that three application contexts will be loaded (one for

each declaration of @ContextConfiguration), and the application context loaded based on the

configuration in AbstractWebTests will be set as the parent context for each of the contexts loaded

for the concrete subclasses.

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextConfiguration("file:src/main/webapp/WEB-INF/applicationContext.xml")

public abstract class AbstractWebTests {}

@ContextHierarchy(@ContextConfiguration("/spring/soap-ws-config.xml")

public class SoapWebServiceTests extends AbstractWebTests {}

@ContextHierarchy(@ContextConfiguration("/spring/rest-ws-config.xml")

public class RestWebServiceTests extends AbstractWebTests {}

The following classes demonstrate the use of named hierarchy levels in order to merge the configuration

for specific levels in a context hierarchy. BaseTests defines two levels in the hierarchy, parent

and child. ExtendedTests extends BaseTests and instructs the Spring TestContext Framework

to merge the context configuration for the child hierarchy level, simply by ensuring that the names

declared via ContextConfiguration's name attribute are both "child". The result is that three

application contexts will be loaded: one for "/app-config.xml", one for "/user-config.xml",

and one for {"/user-config.xml", "/order-config.xml"}. As with the previous example, the

application context loaded from "/app-config.xml" will be set as the parent context for the contexts

loaded from "/user-config.xml" and {"/user-config.xml", "/order-config.xml"}.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextHierarchy({

@ContextConfiguration(name = "parent", locations = "/app-config.xml"),

@ContextConfiguration(name = "child", locations = "/user-config.xml")

})

public class BaseTests {}

@ContextHierarchy(

@ContextConfiguration(name = "child", locations = "/order-config.xml")

)

public class ExtendedTests extends BaseTests {}

In contrast to the previous example, this example demonstrates how to override the configuration for a

given named level in a context hierarchy by setting ContextConfiguration's inheritLocations

flag to false. Consequently, the application context for ExtendedTests will be loaded only from

"/test-user-config.xml" and will have its parent set to the context loaded from "/app-

config.xml".

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 304

@RunWith(SpringJUnit4ClassRunner.class)

@ContextHierarchy({

@ContextConfiguration(name = "parent", locations = "/app-config.xml"),

@ContextConfiguration(name = "child", locations = "/user-config.xml")

})

public class BaseTests {}

@ContextHierarchy(

@ContextConfiguration(

name = "child",

locations = "/test-user-config.xml",

inheritLocations = false

))

public class ExtendedTests extends BaseTests {}

Dirtying a context within a context hierarchy

If @DirtiesContext is used in a test whose context is configured as part of a context hierarchy,

the hierarchyMode flag can be used to control how the context cache is cleared. For further

details consult the discussion of @DirtiesContext in Spring Testing Annotations and the

@DirtiesContext javadocs.

Dependency injection of test fixtures

When you use the DependencyInjectionTestExecutionListener— which is configured by

default — the dependencies of your test instances are injected from beans in the application context that

you configured with @ContextConfiguration. You may use setter injection, field injection, or both,

depending on which annotations you choose and whether you place them on setter methods or fields.

For consistency with the annotation support introduced in Spring 2.5 and 3.0, you can use Spring’s

@Autowired annotation or the @Inject annotation from JSR 300.

Tip

The TestContext framework does not instrument the manner in which a test instance is

instantiated. Thus the use of @Autowired or @Inject for constructors has no effect for test

classes.

Because @Autowired is used to perform autowiring by type, if you have multiple bean definitions

of the same type, you cannot rely on this approach for those particular beans. In that case, you

can use @Autowired in conjunction with @Qualifier. As of Spring 3.0 you may also choose

to use @Inject in conjunction with @Named. Alternatively, if your test class has access to its

ApplicationContext, you can perform an explicit lookup by using (for example) a call to

applicationContext.getBean("titleRepository").

If you do not want dependency injection applied to your test instances, simply do not annotate

fields or setter methods with @Autowired or @Inject. Alternatively, you can disable dependency

injection altogether by explicitly configuring your class with @TestExecutionListeners and omitting

DependencyInjectionTestExecutionListener.class from the list of listeners.

Consider the scenario of testing a HibernateTitleRepository class, as outlined in the Goals

section. The next two code listings demonstrate the use of @Autowired on fields and setter methods.

The application context configuration is presented after all sample code listings.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 305

Note

The dependency injection behavior in the following code listings is not specific to JUnit. The same

DI techniques can be used in conjunction with any testing framework.

The following examples make calls to static assertion methods such as assertNotNull() but

without prepending the call with Assert. In such cases, assume that the method was properly

imported through an import static declaration that is not shown in the example.

The first code listing shows a JUnit-based implementation of the test class that uses @Autowired for

field injection.

@RunWith(SpringJUnit4ClassRunner.class)

// specifies the Spring configuration to load for this test fixture

@ContextConfiguration("repository-config.xml")

public class HibernateTitleRepositoryTests {

// this instance will be dependency injected by type

@Autowired

private HibernateTitleRepository titleRepository;

@Test

public void findById() {

Title title = titleRepository.findById(new Long(10));

assertNotNull(title);

}

Alternatively, you can configure the class to use @Autowired for setter injection as seen below.

@RunWith(SpringJUnit4ClassRunner.class)

// specifies the Spring configuration to load for this test fixture

@ContextConfiguration("repository-config.xml")

public class HibernateTitleRepositoryTests {

// this instance will be dependency injected by type

private HibernateTitleRepository titleRepository;

@Autowired

public void setTitleRepository(HibernateTitleRepository titleRepository) {

this.titleRepository = titleRepository;

}

@Test

public void findById() {

Title title = titleRepository.findById(new Long(10));

assertNotNull(title);

}

The preceding code listings use the same XML context file referenced by the

@ContextConfiguration annotation (that is, repository-config.xml), which looks like this:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 306

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

</bean>

</bean>

</beans>

Note

If you are extending from a Spring-provided test base class that happens to use @Autowired

on one of its setter methods, you might have multiple beans of the affected type defined in your

application context: for example, multiple DataSource beans. In such a case, you can override

the setter method and use the @Qualifier annotation to indicate a specific target bean as

follows, but make sure to delegate to the overridden method in the superclass as well.

// ...

@Autowired

@Override

public void setDataSource(@Qualifier("myDataSource") DataSource dataSource) {

super.setDataSource(dataSource);

}

// ...

The specified qualifier value indicates the specific DataSource bean to inject, narrowing the set

of type matches to a specific bean. Its value is matched against <qualifier> declarations within

the corresponding <bean> definitions. The bean name is used as a fallback qualifier value, so

you may effectively also point to a specific bean by name there (as shown above, assuming that

"myDataSource" is the bean id).

Testing request and session scoped beans

Request and session scoped beans have been supported by Spring for several years now, but it’s

always been a bit non-trivial to test them. As of Spring 3.2 it’s a breeze to test your request-scoped and

session-scoped beans by following these steps.

• Ensure that a WebApplicationContext is loaded for your test by annotating your test class with

@WebAppConfiguration.

• Inject the mock request or session into your test instance and prepare your test fixture as appropriate.

• Invoke your web component that you retrieved from the configured WebApplicationContext (i.e.,

via dependency injection).

• Perform assertions against the mocks.

The following code snippet displays the XML configuration for a login use case. Note that the

userService bean has a dependency on a request-scoped loginAction bean. Also, the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 307

LoginAction is instantiated using SpEL expressions that retrieve the username and password from

the current HTTP request. In our test, we will want to configure these request parameters via the mock

managed by the TestContext framework.

Request-scoped bean configuration.

<beans>

<bean id="userService"

class="com.example.SimpleUserService"

c:loginAction-ref="loginAction" />

<bean id="loginAction" class="com.example.LoginAction"

c:username="{request.getParameter(user)}"

c:password="{request.getParameter(pswd)}"

scope="request">

<aop:scoped-proxy />

</bean>

</beans>

In RequestScopedBeanTests we inject both the UserService (i.e., the subject under test) and the

MockHttpServletRequest into our test instance. Within our requestScope() test method we set

up our test fixture by setting request parameters in the provided MockHttpServletRequest. When

the loginUser() method is invoked on our userService we are assured that the user service has

access to the request-scoped loginAction for the current MockHttpServletRequest (i.e., the one

we just set parameters in). We can then perform assertions against the results based on the known

inputs for the username and password.

Request-scoped bean test.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration

@WebAppConfiguration

public class RequestScopedBeanTests {

@Autowired UserService userService;

@Autowired MockHttpServletRequest request;

@Test

public void requestScope() {

request.setParameter("user", "enigma");

request.setParameter("pswd", "$pr!ng");

LoginResults results = userService.loginUser();

// assert results

}

The following code snippet is similar to the one we saw above for a request-scoped bean; however, this

time the userService bean has a dependency on a session-scoped userPreferences bean. Note

that the UserPreferences bean is instantiated using a SpEL expression that retrieves the theme from

the current HTTP session. In our test, we will need to configure a theme in the mock session managed

by the TestContext framework.

Session-scoped bean configuration.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 308

<beans>

<bean id="userService"

class="com.example.SimpleUserService"

c:userPreferences-ref="userPreferences" />

<bean id="userPreferences"

class="com.example.UserPreferences"

c:theme="#{session.getAttribute(theme)}"

scope="session">

<aop:scoped-proxy />

</bean>

</beans>

In SessionScopedBeanTests we inject the UserService and the MockHttpSession into our test

instance. Within our sessionScope() test method we set up our test fixture by setting the expected

"theme" attribute in the provided MockHttpSession. When the processUserPreferences()

method is invoked on our userService we are assured that the user service has access to the session-

scoped userPreferences for the current MockHttpSession, and we can perform assertions against

the results based on the configured theme.

Session-scoped bean test.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration

@WebAppConfiguration

public class SessionScopedBeanTests {

@Autowired UserService userService;

@Autowired MockHttpSession session;

@Test

public void sessionScope() throws Exception {

session.setAttribute("theme", "blue");

Results results = userService.processUserPreferences();

// assert results

}

Transaction management

In the TestContext framework, transactions are managed by the

TransactionalTestExecutionListener which is configured by default, even if you do not

explicitly declare @TestExecutionListeners on your test class. To enable support for transactions,

however, you must configure a PlatformTransactionManager bean in the ApplicationContext

that is loaded via @ContextConfiguration semantics (further details are provided below). In

addition, you must declare Spring’s @Transactional annotation either at the class or method level

for your tests.

Test-managed transactions

Test-managed transactions are transactions that are managed declaratively via the

TransactionalTestExecutionListener or programmatically via TestTransaction (see

below). Such transactions should not be confused with Spring-managed transactions (i.e., those

managed directly by Spring within the ApplicationContext loaded for tests) or application-

managed transactions (i.e., those managed programmatically within application code that is invoked via

tests). Spring-managed and application-managed transactions will typically participate in test-managed

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 309

transactions; however, caution should be taken if Spring-managed or application-managed transactions

are configured with any propagation type other than REQUIRED or SUPPORTS (see the discussion on

transaction propagation for details).

Enabling and disabling transactions

Annotating a test method with @Transactional causes the test to be run within a transaction that

will, by default, be automatically rolled back after completion of the test. If a test class is annotated

with @Transactional, each test method within that class hierarchy will be run within a transaction.

Test methods that are not annotated with @Transactional (at the class or method level) will not be

run within a transaction. Furthermore, tests that are annotated with @Transactional but have the

propagation type set to NOT_SUPPORTED will not be run within a transaction.

Note that AbstractTransactionalJUnit4SpringContextTests and

AbstractTransactionalTestNGSpringContextTests are preconfigured for transactional

support at the class level.

The following example demonstrates a common scenario for writing an integration test for a

Hibernate-based UserRepository. As explained in the section called “Transaction rollback and

commit behavior”, there is no need to clean up the database after the createUser() method

is executed since any changes made to the database will be automatically rolled back by the

TransactionalTestExecutionListener. See the section called “PetClinic Example” for an

additional example.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(classes = TestConfig.class)

@Transactional

public class HibernateUserRepositoryTests {

@Autowired

HibernateUserRepository repository;

@Autowired

SessionFactory sessionFactory;

JdbcTemplate jdbcTemplate;

@Autowired

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

@Test

public void createUser() {

// track initial state in test database:

final int count = countRowsInTable("user");

User user = new User(...);

repository.save(user);

// Manual flush is required to avoid false positive in test

sessionFactory.getCurrentSession().flush();

assertNumUsers(count + 1);

}

protected int countRowsInTable(String tableName) {

return JdbcTestUtils.countRowsInTable(this.jdbcTemplate, tableName);

}

protected void assertNumUsers(int expected) {

assertEquals("Number of rows in the user table.", expected, countRowsInTable("user"));

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 310

Transaction rollback and commit behavior

By default, test transactions will be automatically rolled back after completion of the test; however,

transactional commit and rollback behavior can be configured declaratively via the class-level

@TransactionConfiguration and method-level @Rollback annotations. See the corresponding

entries in the annotation support section for further details.

Programmatic transaction management

As of Spring Framework 4.1, it is possible to interact with test-managed transactions

programmatically via the static methods in TestTransaction. For example, TestTransaction

may be used within test methods, before methods, and after methods to start or end

the current test-managed transaction or to configure the current test-managed transaction for

rollback or commit. Support for TestTransaction is automatically available whenever the

TransactionalTestExecutionListener is enabled.

The following example demonstrates some of the features of TestTransaction. Consult the javadocs

for TestTransaction for further details.

@ContextConfiguration(classes = TestConfig.class)

public class ProgrammaticTransactionManagementTests extends

AbstractTransactionalJUnit4SpringContextTests {

@Test

public void transactionalTest() {

// assert initial state in test database:

assertNumUsers(2);

deleteFromTables("user");

// changes to the database will be committed!

TestTransaction.flagForCommit();

TestTransaction.end();

assertFalse(TestTransaction.isActive());

assertNumUsers(0);

TestTransaction.start();

// perform other actions against the database that will

// be automatically rolled back after the test completes...

}

protected void assertNumUsers(int expected) {

assertEquals("Number of rows in the user table.", expected, countRowsInTable("user"));

}

Executing code outside of a transaction

Occasionally you need to execute certain code before or after a transactional test method but outside

the transactional context — for example, to verify the initial database state prior to execution of

your test or to verify expected transactional commit behavior after test execution (if the test was

configured not to roll back the transaction). TransactionalTestExecutionListener supports the

@BeforeTransaction and @AfterTransaction annotations exactly for such scenarios. Simply

annotate any public void method in your test class with one of these annotations, and the

TransactionalTestExecutionListener ensures that your before transaction method or after

transaction method is executed at the appropriate time.

Tip

Any before methods (such as methods annotated with JUnit’s @Before) and any after methods

(such as methods annotated with JUnit’s @After) are executed within a transaction. In addition,

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 311

methods annotated with @BeforeTransaction or @AfterTransaction are naturally not

executed for test methods that are not configured to run within a transaction.

Configuring a transaction manager

TransactionalTestExecutionListener expects a PlatformTransactionManager bean

to be defined in the Spring ApplicationContext for the test. In case

there are multiple instances of PlatformTransactionManager within the test’s

ApplicationContext, @TransactionConfiguration supports configuring the bean name

of the PlatformTransactionManager that should be used to drive transactions.

Alternatively, a qualifier may be declared via @Transactional("myQualifier"), or

TransactionManagementConfigurer can be implemented by an @Configuration class. Consult

the javadocs for TestContextTransactionUtils.retrieveTransactionManager() for details

on the algorithm used to look up a transaction manager in the test’s ApplicationContext.

Demonstration of all transaction-related annotations

The following JUnit-based example displays a fictitious integration testing scenario highlighting all

transaction-related annotations. The example is not intended to demonstrate best practices but rather

to demonstrate how these annotations can be used. Consult the annotation support section for further

information and configuration examples. Transaction management for @Sql contains an additional

example using @Sql for declarative SQL script execution with default transaction rollback semantics.

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration

@TransactionConfiguration(transactionManager="txMgr", defaultRollback=false)

@Transactional

public class FictitiousTransactionalTest {

@BeforeTransaction

public void verifyInitialDatabaseState() {

// logic to verify the initial state before a transaction is started

}

@Before

public void setUpTestDataWithinTransaction() {

// set up test data within the transaction

}

@Test

// overrides the class-level defaultRollback setting

@Rollback(true)

public void modifyDatabaseWithinTransaction() {

// logic which uses the test data and modifies database state

}

@After

public void tearDownWithinTransaction() {

// execute "tear down" logic within the transaction

}

@AfterTransaction

public void verifyFinalDatabaseState() {

// logic to verify the final state after transaction has rolled back

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 312

Avoid false positives when testing ORM code

When you test application code that manipulates the state of the Hibernate session, make sure

to flush the underlying session within test methods that execute that code. Failing to flush the

underlying session can produce false positives: your test may pass, but the same code throws an

exception in a live, production environment. In the following Hibernate-based example test case,

one method demonstrates a false positive, and the other method correctly exposes the results of

flushing the session. Note that this applies to JPA and any other ORM frameworks that maintain

an in-memory unit of work.

// ...

@Autowired

private SessionFactory sessionFactory;

@Test // no expected exception!

public void falsePositive() {

updateEntityInHibernateSession();

// False positive: an exception will be thrown once the session is

// finally flushed (i.e., in production code)

}

@Test(expected = GenericJDBCException.class)

public void updateWithSessionFlush() {

updateEntityInHibernateSession();

// Manual flush is required to avoid false positive in test

sessionFactory.getCurrentSession().flush();

}

// ...

Executing SQL scripts

When writing integration tests against a relational database, it is often beneficial to execute SQL scripts

to modify the database schema or insert test data into tables. The spring-jdbc module provides

support for initializing an embedded or existing database by executing SQL scripts when the Spring

ApplicationContext is loaded. See Section 14.8, “Embedded database support” and the section

called “Testing data access logic with an embedded database” for details.

Although it is very useful to initialize a database for testing once when the ApplicationContext is

loaded, sometimes it is essential to be able to modify the database during integration tests. The following

sections explain how to execute SQL scripts programmatically and declaratively during integration tests.

Executing SQL scripts programmatically

Spring provides the following options for executing SQL scripts programmatically within integration test

methods.

•org.springframework.jdbc.datasource.init.ScriptUtils

•org.springframework.jdbc.datasource.init.ResourceDatabasePopulator

•org.springframework.test.context.junit4.AbstractTransactionalJUnit4SpringContextTests

•org.springframework.test.context.testng.AbstractTransactionalTestNGSpringContextTests

ScriptUtils provides a collection of static utility methods for working with SQL scripts and is mainly

intended for internal use within the framework. However, if you require full control over how SQL scripts

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 313

are parsed and executed, ScriptUtils may suit your needs better than some of the other alternatives

described below. Consult the javadocs for individual methods in ScriptUtils for further details.

ResourceDatabasePopulator provides a simple object-based API for programmatically populating,

initializing, or cleaning up a database using SQL scripts defined in external resources.

ResourceDatabasePopulator provides options for configuring the character encoding, statement

separator, comment delimiters, and error handling flags used when parsing and executing the scripts,

and each of the configuration options has a reasonable default value. Consult the javadocs for

details on default values. To execute the scripts configured in a ResourceDatabasePopulator,

you can invoke either the populate(Connection) method to execute the populator against a

java.sql.Connection or the execute(DataSource) method to execute the populator against a

javax.sql.DataSource. The following example specifies SQL scripts for a test schema and test

data, sets the statement separator to "@@", and then executes the scripts against a DataSource.

@Test

public void databaseTest {

ResourceDatabasePopulator populator = new ResourceDatabasePopulator();

populator.addScripts(

new ClassPathResource("test-schema.sql"),

new ClassPathResource("test-data.sql"));

populator.setSeparator("@@");

populator.execute(this.dataSource);

// execute code that uses the test schema and data

}

Note that ResourceDatabasePopulator internally delegates to ScriptUtils for

parsing and executing SQL scripts. Similarly, the executeSqlScript(..) methods in

AbstractTransactionalJUnit4SpringContextTests and

AbstractTransactionalTestNGSpringContextTests internally use a

ResourceDatabasePopulator for executing SQL scripts. Consult the javadocs for the various

executeSqlScript(..) methods for further details.

Executing SQL scripts declaratively with @Sql

In addition to the aforementioned mechanisms for executing SQL scripts programmatically, SQL scripts

can also be configured declaratively in the Spring TestContext Framework. Specifically, the @Sql

annotation can be declared on a test class or test method to configure the resource paths to SQL scripts

that should be executed against a given database either before or after an integration test method. Note

that method-level declarations override class-level declarations and that support for @Sql is provided

by the SqlScriptsTestExecutionListener which is enabled by default.

Path resource semantics

Each path will be interpreted as a Spring Resource. A plain path — for example, "schema.sql"— will

be treated as a classpath resource that is relative to the package in which the test class is defined.

A path starting with a slash will be treated as an absolute classpath resource, for example: "/org/

example/schema.sql". A path which references a URL (e.g., a path prefixed with classpath:,

file:, http:, etc.) will be loaded using the specified resource protocol.

The following example demonstrates how to use @Sql at the class level and at the method level within

a JUnit-based integration test class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 314

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration

@Sql("/test-schema.sql")

public class DatabaseTests {

@Test

public void emptySchemaTest {

// execute code that uses the test schema without any test data

}

@Test

@Sql({"/test-schema.sql", "/test-user-data.sql"})

public void userTest {

// execute code that uses the test schema and test data

}

Default script detection

If no SQL scripts are specified, an attempt will be made to detect a default script depending on where

@Sql is declared. If a default cannot be detected, an IllegalStateException will be thrown.

•class-level declaration: if the annotated test class is com.example.MyTest, the corresponding

default script is "classpath:com/example/MyTest.sql".

•method-level declaration: if the annotated test method is named testMethod() and is defined in

the class com.example.MyTest, the corresponding default script is "classpath:com/example/

MyTest.testMethod.sql".

Declaring multiple @Sql sets

If multiple sets of SQL scripts need to be configured for a given test class or test method but with

different syntax configuration, different error handling rules, or different execution phases per set, it

is possible to declare multiple instances of @Sql. With Java 8, @Sql can be used as a repeatable

annotation. Otherwise, the @SqlGroup annotation can be used as an explicit container for declaring

multiple instances of @Sql.

The following example demonstrates the use of @Sql as a repeatable annotation using Java 8. In this

scenario the test-schema.sql script uses a different syntax for single-line comments.

@Test

@Sql(scripts = "/test-schema.sql", config = @SqlConfig(commentPrefix = "`"))

@Sql("/test-user-data.sql")

public void userTest {

// execute code that uses the test schema and test data

}

The following example is identical to the above except that the @Sql declarations are grouped together

within @SqlGroup for compatibility with Java 6 and Java 7.

@Test

@SqlGroup({

@Sql(scripts = "/test-schema.sql", config = @SqlConfig(commentPrefix = "`")),

@Sql("/test-user-data.sql")

)}

public void userTest {

// execute code that uses the test schema and test data

}

Script execution phases

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 315

By default, SQL scripts will be executed before the corresponding test method. However, if a particular

set of scripts needs to be executed after the test method — for example, to clean up database

state — the executionPhase attribute in @Sql can be used as seen in the following example. Note

that ISOLATED and AFTER_TEST_METHOD are statically imported from Sql.TransactionMode and

Sql.ExecutionPhase respectively.

@Test

@Sql(

scripts = "create-test-data.sql",

config = @SqlConfig(transactionMode = ISOLATED)

)

@Sql(

scripts = "delete-test-data.sql",

config = @SqlConfig(transactionMode = ISOLATED),

executionPhase = AFTER_TEST_METHOD

)

public void userTest {

// execute code that needs the test data to be committed

// to the database outside of the test's transaction

}

Script configuration with @SqlConfig

Configuration for script parsing and error handling can be configured via the @SqlConfig annotation.

When declared as a class-level annotation on an integration test class, @SqlConfig serves as global

configuration for all SQL scripts within the test class hierarchy. When declared directly via the config

attribute of the @Sql annotation, @SqlConfig serves as local configuration for the SQL scripts declared

within the enclosing @Sql annotation. Every attribute in @SqlConfig has an implicit default value which

is documented in the javadocs of the corresponding attribute. Due to the rules defined for annotation

attributes in the Java Language Specification, it is unfortunately not possible to assign a value of

null to an annotation attribute. Thus, in order to support overrides of inherited global configuration,

@SqlConfig attributes have an explicit default value of either "" for Strings or DEFAULT for Enums.

This approach allows local declarations of @SqlConfig to selectively override individual attributes

from global declarations of @SqlConfig by providing a value other than "" or DEFAULT. Global

@SqlConfig attributes are inherited whenever local @SqlConfig attributes do not supply an explicit

value other than "" or DEFAULT. Explicit local configuration therefore overrides global configuration.

The configuration options provided by @Sql and @SqlConfig are equivalent to those supported

by ScriptUtils and ResourceDatabasePopulator but are a superset of those provided by

the <jdbc:initialize-database/> XML namespace element. Consult the javadocs of individual

attributes in @Sql and @SqlConfig for details.

Transaction management for @Sql

By default, the SqlScriptsTestExecutionListener will infer the desired transaction semantics

for scripts configured via @Sql. Specifically, SQL scripts will be executed without a transaction,

within an existing Spring-managed transaction — for example, a transaction managed by the

TransactionalTestExecutionListener for a test annotated with @Transactional— or

within an isolated transaction, depending on the configured value of the transactionMode

attribute in @SqlConfig and the presence of a PlatformTransactionManager in the test’s

ApplicationContext. As a bare minimum however, a javax.sql.DataSource must be present

in the test’s ApplicationContext.

If the algorithms used by SqlScriptsTestExecutionListener to detect a DataSource and

PlatformTransactionManager and infer the transaction semantics do not suit your needs,

you may specify explicit names via the dataSource and transactionManager attributes

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 316

of @SqlConfig. Furthermore, the transaction propagation behavior can be controlled via the

transactionMode attribute of @SqlConfig— for example, if scripts should be executed in

an isolated transaction. Although a thorough discussion of all supported options for transaction

management with @Sql is beyond the scope of this reference manual, the javadocs for @SqlConfig

and SqlScriptsTestExecutionListener provide detailed information, and the following example

demonstrates a typical testing scenario using JUnit and transactional tests with @Sql. Note that there

is no need to clean up the database after the usersTest() method is executed since any changes

made to the database (either within the the test method or within the /test-data.sql script) will

be automatically rolled back by the TransactionalTestExecutionListener (see transaction

management for details).

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(classes = TestDatabaseConfig.class)

@Transactional

public class TransactionalSqlScriptsTests {

protected JdbcTemplate jdbcTemplate;

@Autowired

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

@Test

@Sql("/test-data.sql")

public void usersTest() {

// verify state in test database:

assertNumUsers(2);

// execute code that uses the test data...

}

protected int countRowsInTable(String tableName) {

return JdbcTestUtils.countRowsInTable(this.jdbcTemplate, tableName);

}

protected void assertNumUsers(int expected) {

assertEquals("Number of rows in the user table.", expected, countRowsInTable("user"));

}

TestContext Framework support classes

JUnit support classes

The org.springframework.test.context.junit4 package provides the following support

classes for JUnit-based test cases.

•AbstractJUnit4SpringContextTests

•AbstractTransactionalJUnit4SpringContextTests

AbstractJUnit4SpringContextTests is an abstract base test class that integrates the Spring

TestContext Framework with explicit ApplicationContext testing support in a JUnit 4.9+

environment. When you extend AbstractJUnit4SpringContextTests, you can access a

protected applicationContext instance variable that can be used to perform explicit bean

lookups or to test the state of the context as a whole.

AbstractTransactionalJUnit4SpringContextTests is an abstract transactional extension

of AbstractJUnit4SpringContextTests that adds some convenience functionality

for JDBC access. This class expects a javax.sql.DataSource bean and a

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 317

PlatformTransactionManager bean to be defined in the ApplicationContext. When you

extend AbstractTransactionalJUnit4SpringContextTests you can access a protected

jdbcTemplate instance variable that can be used to execute SQL statements to query

the database. Such queries can be used to confirm database state both prior to and after

execution of database-related application code, and Spring ensures that such queries run

in the scope of the same transaction as the application code. When used in conjunction

with an ORM tool, be sure to avoid false positives. As mentioned in the section called

“JDBC Testing Support”, AbstractTransactionalJUnit4SpringContextTests also provides

convenience methods which delegate to methods in JdbcTestUtils using the aforementioned

jdbcTemplate. Furthermore, AbstractTransactionalJUnit4SpringContextTests provides

an executeSqlScript(..) method for executing SQL scripts against the configured DataSource.

Tip

These classes are a convenience for extension. If you do not want your test classes to be

tied to a Spring-specific class hierarchy, you can configure your own custom test classes

by using @RunWith(SpringJUnit4ClassRunner.class), @ContextConfiguration,

@TestExecutionListeners, and so on.

Spring JUnit Runner

The Spring TestContext Framework offers full integration with JUnit 4.9+ through

a custom runner (tested on JUnit 4.9 — 4.11). By annotating test classes with

@RunWith(SpringJUnit4ClassRunner.class), developers can implement standard JUnit-based

unit and integration tests and simultaneously reap the benefits of the TestContext framework such

as support for loading application contexts, dependency injection of test instances, transactional

test method execution, and so on. The following code listing displays the minimal requirements for

configuring a test class to run with the custom Spring Runner. @TestExecutionListeners is

configured with an empty list in order to disable the default listeners, which otherwise would require an

ApplicationContext to be configured through @ContextConfiguration.

@RunWith(SpringJUnit4ClassRunner.class)

@TestExecutionListeners({})

public class SimpleTest {

@Test

public void testMethod() {

// execute test logic...

}

TestNG support classes

The org.springframework.test.context.testng package provides the following support

classes for TestNG based test cases.

•AbstractTestNGSpringContextTests

•AbstractTransactionalTestNGSpringContextTests

AbstractTestNGSpringContextTests is an abstract base test class that integrates the Spring

TestContext Framework with explicit ApplicationContext testing support in a TestNG environment.

When you extend AbstractTestNGSpringContextTests, you can access a protected

applicationContext instance variable that can be used to perform explicit bean lookups or to test

the state of the context as a whole.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 318

AbstractTransactionalTestNGSpringContextTests is an abstract transactional extension

of AbstractTestNGSpringContextTests that adds some convenience functionality

for JDBC access. This class expects a javax.sql.DataSource bean and a

PlatformTransactionManager bean to be defined in the ApplicationContext. When you

extend AbstractTransactionalTestNGSpringContextTests you can access a protected

jdbcTemplate instance variable that can be used to execute SQL statements to query

the database. Such queries can be used to confirm database state both prior to and after

execution of database-related application code, and Spring ensures that such queries run

in the scope of the same transaction as the application code. When used in conjunction

with an ORM tool, be sure to avoid false positives. As mentioned in the section called

“JDBC Testing Support”, AbstractTransactionalTestNGSpringContextTests also provides

convenience methods which delegate to methods in JdbcTestUtils using the aforementioned

jdbcTemplate. Furthermore, AbstractTransactionalTestNGSpringContextTests provides

an executeSqlScript(..) method for executing SQL scripts against the configured DataSource.

Tip

These classes are a convenience for extension. If you do not want your test classes to be

tied to a Spring-specific class hierarchy, you can configure your own custom test classes

by using @ContextConfiguration, @TestExecutionListeners, and so on, and by

manually instrumenting your test class with a TestContextManager. See the source code of

AbstractTestNGSpringContextTests for an example of how to instrument your test class.

Spring MVC Test Framework

Standalone project

Before inclusion in Spring Framework 3.2, the Spring MVC Test framework had already existed

as a separate project on GitHub where it grew and evolved through actual use, feedback, and the

contribution of many.

The standalone spring-test-mvc project is still available on GitHub and can be used in conjunction

with Spring Framework 3.1.x. Applications upgrading to 3.2 or later should replace the spring-

test-mvc dependency with a dependency on spring-test.

The spring-test module uses a different package org.springframework.test.web but

otherwise is nearly identical with two exceptions. One is support for features new in 3.2 (e.g.

asynchronous web requests). The other relates to the options for creating a MockMvc instance. In

Spring Framework 3.2 and later, this can only be done through the TestContext framework, which

provides caching benefits for the loaded configuration.

The Spring MVC Test framework provides first class JUnit support for testing client and server-side

Spring MVC code through a fluent API. Typically it loads the actual Spring configuration through

the TestContext framework and always uses the DispatcherServlet to process requests thus

approximating full integration tests without requiring a running Servlet container.

Client-side tests are RestTemplate-based and allow tests for code that relies on the RestTemplate

without requiring a running server to respond to the requests.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 319

Server-Side Tests

Before Spring Framework 3.2, the most likely way to test a Spring MVC controller was to write a unit

test that instantiates the controller, injects it with mock or stub dependencies, and then calls its methods

directly, using a MockHttpServletRequest and MockHttpServletResponse where necessary.

Although this is pretty easy to do, controllers have many annotations, and much remains untested.

Request mappings, data binding, type conversion, and validation are just a few examples of what

isn’t tested. Furthermore, there are other types of annotated methods such as @InitBinder,

@ModelAttribute, and @ExceptionHandler that get invoked as part of request processing.

The idea behind Spring MVC Test is to be able to re-write those controller tests by performing

actual requests and generating responses, as they would be at runtime, along the way invoking

controllers through the Spring MVC DispatcherServlet. Controllers can still be injected with mock

dependencies, so tests can remain focused on the web layer.

Spring MVC Test builds on the familiar "mock" implementations of the Servlet API available in the

spring-test module. This allows performing requests and generating responses without the need

for running in a Servlet container. For the most part everything should work as it does at runtime with

the exception of JSP rendering, which is not available outside a Servlet container. Furthermore, if you

are familiar with how the MockHttpServletResponse works, you’ll know that forwards and redirects

are not actually executed. Instead "forwarded" and "redirected" URLs are saved and can be asserted in

tests. This means if you are using JSPs, you can verify the JSP page to which the request was forwarded.

All other means of rendering including @ResponseBody methods and View types (besides JSPs) such

as Freemarker, Velocity, Thymeleaf, and others for rendering HTML, JSON, XML, and so on should

work as expected, and the response will contain the generated content.

Below is an example of a test requesting account information in JSON format:

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;

import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextConfiguration("test-servlet-context.xml")

public class ExampleTests {

@Autowired

private WebApplicationContext wac;

private MockMvc mockMvc;

@Before

public void setup() {

this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();

}

@Test

public void getAccount() throws Exception {

this.mockMvc.perform(get("/accounts/1").accept(MediaType.parseMediaType("application/

json;charset=UTF-8")))

.andExpect(status().isOk())

.andExpect(content().contentType("application/json"))

.andExpect(jsonPath("$.name").value("Lee"));

}

The test relies on the WebApplicationContext support of the TestContext framework. It loads Spring

configuration from an XML configuration file located in the same package as the test class (also supports

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 320

JavaConfig) and injects the created WebApplicationContext into the test so a MockMvc instance

can be created with it.

The MockMvc is then used to perform a request to "/accounts/1" and verify the resulting response

status is 200, the response content type is "application/json", and response content has a JSON

property called "name" with the value "Lee". JSON content is inspected with the help of Jayway’s

JsonPath project. There are lots of other options for verifying the result of the performed request and

those will be discussed later.

Static Imports

The fluent API in the example above requires a few static imports such as

MockMvcRequestBuilders.*, MockMvcResultMatchers.*, and MockMvcBuilders.*. An

easy way to find these classes is to search for types matching "MockMvc*". If using Eclipse, be sure to

add them as "favorite static members" in the Eclipse preferences underJava # Editor # Content Assist #

Favorites. That will allow use of content assist after typing the first character of the static method name.

Other IDEs (e.g. IntelliJ) may not require any additional configuration. Just check the support for code

completion on static members.

Setup Options

The goal of server-side test setup is to create an instance of MockMvc that can be used to perform

requests. There are two main options.

The first option is to point to Spring MVC configuration through the TestContext framework, which

loads the Spring configuration and injects a WebApplicationContext into the test to use to create

a MockMvc:

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextConfiguration("my-servlet-context.xml")

public class MyWebTests {

@Autowired

private WebApplicationContext wac;

private MockMvc mockMvc;

@Before

public void setup() {

this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();

}

// ...

}

The second option is to simply register a controller instance without loading any Spring configuration.

Instead basic Spring MVC configuration suitable for testing annotated controllers is automatically

created. The created configuration is comparable to that of the MVC JavaConfig (and the MVC

namespace) and can be customized to a degree through builder-style methods:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 321

public class MyWebTests {

private MockMvc mockMvc;

@Before

public void setup() {

this.mockMvc = MockMvcBuilders.standaloneSetup(new AccountController()).build();

}

// ...

}

Which option should you use?

The "webAppContextSetup" loads the actual Spring MVC configuration resulting in a more complete

integration test. Since the TestContext framework caches the loaded Spring configuration, it helps to

keep tests running fast even as more tests get added. Furthermore, you can inject mock services into

controllers through Spring configuration, in order to remain focused on testing the web layer. Here is an

example of declaring a mock service with Mockito:

<constructor-arg value="org.example.AccountService"/>

</bean>

Then you can inject the mock service into the test in order set up and verify expectations:

@RunWith(SpringJUnit4ClassRunner.class)

@WebAppConfiguration

@ContextConfiguration("test-servlet-context.xml")

public class AccountTests {

@Autowired

private WebApplicationContext wac;

private MockMvc mockMvc;

@Autowired

private AccountService accountService;

// ...

}

The "standaloneSetup" on the other hand is a little closer to a unit test. It tests one controller at a

time, the controller can be injected with mock dependencies manually, and it doesn’t involve loading

Spring configuration. Such tests are more focused in style and make it easier to see which controller

is being tested, whether any specific Spring MVC configuration is required to work, and so on. The

"standaloneSetup" is also a very convenient way to write ad-hoc tests to verify some behavior or to

debug an issue.

Just like with integration vs unit testing, there is no right or wrong answer. Using the "standaloneSetup"

does imply the need for some additional "webAppContextSetup" tests to verify the Spring MVC

configuration. Alternatively, you can decide write all tests with "webAppContextSetup" and always test

against actual Spring MVC configuration.

Performing Requests

To perform requests, use the appropriate HTTP method and additional builder-style methods

corresponding to properties of MockHttpServletRequest. For example:

mockMvc.perform(post("/hotels/{id}", 42).accept(MediaType.APPLICATION_JSON));

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 322

In addition to all the HTTP methods, you can also perform file upload requests, which internally creates

an instance of MockMultipartHttpServletRequest:

mockMvc.perform(fileUpload("/doc").file("a1", "ABC".getBytes("UTF-8")));

Query string parameters can be specified in the URI template:

mockMvc.perform(get("/hotels?foo={foo}", "bar"));

Or by adding Servlet request parameters:

mockMvc.perform(get("/hotels").param("foo", "bar"));

If application code relies on Servlet request parameters, and doesn’t check the query string, as is most

often the case, then it doesn’t matter how parameters are added. Keep in mind though that parameters

provided in the URI template will be decoded while parameters provided through the param(...)

method are expected to be decoded.

In most cases it’s preferable to leave out the context path and the Servlet path from the request URI. If

you must test with the full request URI, be sure to set the contextPath and servletPath accordingly

so that request mappings will work:

mockMvc.perform(get("/app/main/hotels/{id}").contextPath("/app").servletPath("/main"))

Looking at the above example, it would be cumbersome to set the contextPath and servletPath with

every performed request. That’s why you can define default request properties when building the

MockMvc:

public class MyWebTests {

private MockMvc mockMvc;

@Before

public void setup() {

mockMvc = standaloneSetup(new AccountController())

.defaultRequest(get("/")

.contextPath("/app").servletPath("/main")

.accept(MediaType.APPLICATION_JSON).build();

}

The above properties will apply to every request performed through the MockMvc. If the same property

is also specified on a given request, it will override the default value. That is why, the HTTP method and

URI don’t matter, when setting default request properties, since they must be specified on every request.

Defining Expectations

Expectations can be defined by appending one or more .andExpect(..) after call to perform the

request:

mockMvc.perform(get("/accounts/1")).andExpect(status().isOk());

MockMvcResultMatchers.* defines a number of static members, some of which return types with

additional methods, for asserting the result of the performed request. The assertions fall in two general

categories.

The first category of assertions verify properties of the response, i.e the response status, headers, and

content. Those are the most important things to test for.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 323

The second category of assertions go beyond the response, and allow inspecting Spring MVC specific

constructs such as which controller method processed the request, whether an exception was raised

and handled, what the content of the model is, what view was selected, what flash attributes were added,

and so on. It is also possible to verify Servlet specific constructs such as request and session attributes.

The following test asserts that binding/validation failed:

mockMvc.perform(post("/persons"))

.andExpect(status().isOk())

.andExpect(model().attributeHasErrors("person"));

Many times when writing tests, it’s useful to dump the result of the performed request. This can be done

as follows, where print() is a static import from MockMvcResultHandlers:

mockMvc.perform(post("/persons"))

.andDo(print())

.andExpect(status().isOk())

.andExpect(model().attributeHasErrors("person"));

As long as request processing causes an unhandled exception, the print() method will print all the

available result data to System.out.

In some cases, you may want to get direct access to the result and verify something that cannot be

verified otherwise. This can be done by appending .andReturn() at the end after all expectations:

MvcResult mvcResult = mockMvc.perform(post("/persons")).andExpect(status().isOk()).andReturn();

// ...

When all tests repeat the same expectations, you can define the common expectations once when

building the MockMvc:

standaloneSetup(new SimpleController())

.alwaysExpect(status().isOk())

.alwaysExpect(content().contentType("application/json;charset=UTF-8"))

.build()

Note that the expectation is always applied and cannot be overridden without creating a separate

MockMvc instance.

When JSON response content contains hypermedia links created with Spring HATEOAS, the resulting

links can be verified:

mockMvc.perform(get("/people").accept(MediaType.APPLICATION_JSON))

.andExpect(jsonPath("$.links[?(@.rel == self)].href").value("http://localhost:8080/people"));

When XML response content contains hypermedia links created with Spring HATEOAS, the resulting

links can be verified:

Map<String, String> ns = Collections.singletonMap("ns", "http://www.w3.org/2005/Atom");

mockMvc.perform(get("/handle").accept(MediaType.APPLICATION_XML))

.andExpect(xpath("/person/ns:link[@rel=self]/@href", ns).string("http://localhost:8080/people"));

Filter Registrations

When setting up a MockMvc, you can register one or more Filter instances:

mockMvc = standaloneSetup(new PersonController()).addFilters(new CharacterEncodingFilter()).build();

Registered filters will be invoked through MockFilterChain from spring-test and the last filter will

delegates to the DispatcherServlet.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 324

Further Server-Side Test Examples

The framework’s own tests include many sample tests intended to demonstrate how to use Spring MVC

Test. Browse these examples for further ideas. Also the spring-mvc-showcase has full test coverage

based on Spring MVC Test.

Client-Side REST Tests

Client-side tests are for code using the RestTemplate. The goal is to define expected requests and

provide "stub" responses:

RestTemplate restTemplate = new RestTemplate();

MockRestServiceServer mockServer = MockRestServiceServer.createServer(restTemplate);

mockServer.expect(requestTo("/greeting")).andRespond(withSuccess("Hello world", MediaType.TEXT_PLAIN));

// use RestTemplate ...

mockServer.verify();

In the above example, MockRestServiceServer — the central class for client-side REST

tests — configures the RestTemplate with a custom ClientHttpRequestFactory that asserts

actual requests against expectations and returns "stub" responses. In this case we expect a single

request to "/greeting" and want to return a 200 response with "text/plain" content. We could define as

many additional requests and stub responses as necessary.

Once expected requests and stub responses have been defined, the RestTemplate can be used in

client-side code as usual. At the end of the tests mockServer.verify() can be used to verify that

all expected requests were performed.

Static Imports

Just like with server-side tests, the fluent API for client-side tests requires a few static imports. Those are

easy to find by searching "MockRest*". Eclipse users should add "MockRestRequestMatchers.*"

and "MockRestResponseCreators.*" as "favorite static members" in the Eclipse preferences under

Java # Editor # Content Assist # Favorites. That allows using content assist after typing the first character

of the static method name. Other IDEs (e.g. IntelliJ) may not require any additional configuration. Just

check the support for code completion on static members.

Further Examples of Client-side REST Tests

Spring MVC Test’s own tests include example tests of client-side REST tests.

PetClinic Example

The PetClinic application, available on GitHub, illustrates several features of the Spring TestContext

Framework in a JUnit environment. Most test functionality is included in the AbstractClinicTests,

for which a partial listing is shown below:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 325

import static org.junit.Assert.assertEquals;

// import ...

@ContextConfiguration

public abstract class AbstractClinicTests extends AbstractTransactionalJUnit4SpringContextTests {

@Autowired

protected Clinic clinic;

@Test

public void getVets() {

Collection<Vet> vets = this.clinic.getVets();

assertEquals("JDBC query must show the same number of vets",

super.countRowsInTable("VETS"), vets.size());

Vet v1 = EntityUtils.getById(vets, Vet.class, 2);

assertEquals("Leary", v1.getLastName());

assertEquals(1, v1.getNrOfSpecialties());

assertEquals("radiology", (v1.getSpecialties().get(0)).getName());

// ...

}

// ...

}

Notes:

• This test case extends the AbstractTransactionalJUnit4SpringContextTests

class, from which it inherits configuration for Dependency Injection (through the

DependencyInjectionTestExecutionListener) and transactional behavior (through the

TransactionalTestExecutionListener).

• The clinic instance variable — the application object being tested — is set by Dependency Injection

through @Autowired semantics.

• The getVets() method illustrates how you can use the inherited countRowsInTable() method

to easily verify the number of rows in a given table, thus verifying correct behavior of the application

code being tested. This allows for stronger tests and lessens dependency on the exact test data. For

example, you can add additional rows in the database without breaking tests.

• Like many integration tests that use a database, most of the tests in AbstractClinicTests depend

on a minimum amount of data already in the database before the test cases run. Alternatively, you

might choose to populate the database within the test fixture set up of your test cases — again, within

the same transaction as the tests.

The PetClinic application supports three data access technologies: JDBC, Hibernate, and

JPA. By declaring @ContextConfiguration without any specific resource locations, the

AbstractClinicTests class will have its application context loaded from the default location,

AbstractClinicTests-context.xml, which declares a common DataSource. Subclasses

specify additional context locations that must declare a PlatformTransactionManager and a

concrete implementation of Clinic.

For example, the Hibernate implementation of the PetClinic tests contains the following

implementation. For this example, HibernateClinicTests does not contain a single line of

code: we only need to declare @ContextConfiguration, and the tests are inherited from

AbstractClinicTests. Because @ContextConfiguration is declared without any specific

resource locations, the Spring TestContext Framework loads an application context from all

the beans defined in AbstractClinicTests-context.xml (i.e., the inherited locations) and

HibernateClinicTests-context.xml, with HibernateClinicTests-context.xml possibly

overriding beans defined in AbstractClinicTests-context.xml.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 326

@ContextConfiguration

public class HibernateClinicTests extends AbstractClinicTests { }

In a large-scale application, the Spring configuration is often split across multiple files. Consequently,

configuration locations are typically specified in a common base class for all application-specific

integration tests. Such a base class may also add useful instance variables — populated by Dependency

Injection, naturally — such as a SessionFactory in the case of an application using Hibernate.

As far as possible, you should have exactly the same Spring configuration files in your integration

tests as in the deployed environment. One likely point of difference concerns database connection

pooling and transaction infrastructure. If you are deploying to a full-blown application server,

you will probably use its connection pool (available through JNDI) and JTA implementation.

Thus in production you will use a JndiObjectFactoryBean or <jee:jndi-lookup> for the

DataSource and JtaTransactionManager. JNDI and JTA will not be available in out-of-container

integration tests, so you should use a combination like the Commons DBCP BasicDataSource and

DataSourceTransactionManager or HibernateTransactionManager for them. You can factor

out this variant behavior into a single XML file, having the choice between application server and a local

configuration separated from all other configuration, which will not vary between the test and production

environments. In addition, it is advisable to use properties files for connection settings. See the PetClinic

application for an example.

11.4 Further Resources

Consult the following resources for more information about testing:

•JUnit: "A programmer-oriented testing framework for Java". Used by the Spring Framework in its test

suite.

•TestNG: A testing framework inspired by JUnit with added support for annotations, test groups, data-

driven testing, distributed testing, etc.

•MockObjects.com: Web site dedicated to mock objects, a technique for improving the design of code

within test-driven development.

•"Mock Objects": Article in Wikipedia.

•EasyMock: Java library " that provides Mock Objects for interfaces (and objects through the class

extension) by generating them on the fly using Java’s proxy mechanism. " Used by the Spring

Framework in its test suite.

•JMock: Library that supports test-driven development of Java code with mock objects.

•Mockito: Java mock library based on the test spy pattern.

•DbUnit: JUnit extension (also usable with Ant and Maven) targeted for database-driven projects that,

among other things, puts your database into a known state between test runs.

•The Grinder: Java load testing framework.

Part IV. Data Access

This part of the reference documentation is concerned with data access and the interaction between

the data access layer and the business or service layer.

Spring’s comprehensive transaction management support is covered in some detail, followed by

thorough coverage of the various data access frameworks and technologies that the Spring Framework

integrates with.

• Chapter 12, Transaction Management

• Chapter 13, DAO support

• Chapter 14, Data access with JDBC

• Chapter 15, Object Relational Mapping (ORM) Data Access

• Chapter 16, Marshalling XML using O/X Mappers

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 328

12. Transaction Management

12.1 Introduction to Spring Framework transaction

management

Comprehensive transaction support is among the most compelling reasons to use the Spring

Framework. The Spring Framework provides a consistent abstraction for transaction management that

delivers the following benefits:

• Consistent programming model across different transaction APIs such as Java Transaction API (JTA),

JDBC, Hibernate, Java Persistence API (JPA), and Java Data Objects (JDO).

• Support for declarative transaction management.

• Simpler API for programmatic transaction management than complex transaction APIs such as JTA.

• Excellent integration with Spring’s data access abstractions.

The following sections describe the Spring Framework’s transaction value-adds and technologies. (The

chapter also includes discussions of best practices, application server integration, and solutions to

common problems.)

•Advantages of the Spring Framework’s transaction support model describes why you would use the

Spring Framework’s transaction abstraction instead of EJB Container-Managed Transactions (CMT)

or choosing to drive local transactions through a proprietary API such as Hibernate.

•Understanding the Spring Framework transaction abstraction outlines the core classes and describes

how to configure and obtain DataSource instances from a variety of sources.

•Synchronizing resources with transactionsdescribes how the application code ensures that resources

are created, reused, and cleaned up properly.

•Declarative transaction management describes support for declarative transaction management.

•Programmatic transaction management covers support for programmatic (that is, explicitly coded)

transaction management.

12.2 Advantages of the Spring Framework’s transaction

support model

Traditionally, Java EE developers have had two choices for transaction management: global or local

transactions, both of which have profound limitations. Global and local transaction management is

reviewed in the next two sections, followed by a discussion of how the Spring Framework’s transaction

management support addresses the limitations of the global and local transaction models.

Global transactions

Global transactions enable you to work with multiple transactional resources, typically relational

databases and message queues. The application server manages global transactions through the

JTA, which is a cumbersome API to use (partly due to its exception model). Furthermore, a JTA

UserTransaction normally needs to be sourced from JNDI, meaning that you also need to use JNDI

in order to use JTA. Obviously the use of global transactions would limit any potential reuse of application

code, as JTA is normally only available in an application server environment.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 329

Previously, the preferred way to use global transactions was via EJB CMT (Container Managed

Transaction): CMT is a form of declarative transaction management (as distinguished from

programmatic transaction management). EJB CMT removes the need for transaction-related JNDI

lookups, although of course the use of EJB itself necessitates the use of JNDI. It removes most but

not all of the need to write Java code to control transactions. The significant downside is that CMT is

tied to JTA and an application server environment. Also, it is only available if one chooses to implement

business logic in EJBs, or at least behind a transactional EJB facade. The negatives of EJB in general

are so great that this is not an attractive proposition, especially in the face of compelling alternatives

for declarative transaction management.

Local transactions

Local transactions are resource-specific, such as a transaction associated with a JDBC connection.

Local transactions may be easier to use, but have significant disadvantages: they cannot work

across multiple transactional resources. For example, code that manages transactions using a JDBC

connection cannot run within a global JTA transaction. Because the application server is not involved in

transaction management, it cannot help ensure correctness across multiple resources. (It is worth noting

that most applications use a single transaction resource.) Another downside is that local transactions

are invasive to the programming model.

Spring Framework’s consistent programming model

Spring resolves the disadvantages of global and local transactions. It enables application developers to

use a consistent programming model in any environment. You write your code once, and it can benefit

from different transaction management strategies in different environments. The Spring Framework

provides both declarative and programmatic transaction management. Most users prefer declarative

transaction management, which is recommended in most cases.

With programmatic transaction management, developers work with the Spring Framework transaction

abstraction, which can run over any underlying transaction infrastructure. With the preferred declarative

model, developers typically write little or no code related to transaction management, and hence do not

depend on the Spring Framework transaction API, or any other transaction API.

Do you need an application server for transaction management?

The Spring Framework’s transaction management support changes traditional rules as to when

an enterprise Java application requires an application server.

In particular, you do not need an application server simply for declarative transactions through

EJBs. In fact, even if your application server has powerful JTA capabilities, you may decide

that the Spring Framework’s declarative transactions offer more power and a more productive

programming model than EJB CMT.

Typically you need an application server’s JTA capability only if your application needs to handle

transactions across multiple resources, which is not a requirement for many applications. Many

high-end applications use a single, highly scalable database (such as Oracle RAC) instead.

Standalone transaction managers such as Atomikos Transactions and JOTM are other options. Of

course, you may need other application server capabilities such as Java Message Service (JMS)

and Java EE Connector Architecture (JCA).

The Spring Framework gives you the choice of when to scale your application to a fully loaded

application server. Gone are the days when the only alternative to using EJB CMT or JTA was

to write code with local transactions such as those on JDBC connections, and face a hefty

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 330

rework if you need that code to run within global, container-managed transactions. With the Spring

Framework, only some of the bean definitions in your configuration file, rather than your code,

need to change.

12.3 Understanding the Spring Framework transaction

abstraction

The key to the Spring transaction abstraction is the notion of

a transaction strategy. A transaction strategy is defined by the

org.springframework.transaction.PlatformTransactionManager interface:

public interface PlatformTransactionManager {

TransactionStatus getTransaction(

TransactionDefinition definition) throws TransactionException;

void commit(TransactionStatus status) throws TransactionException;

void rollback(TransactionStatus status) throws TransactionException;

}

This is primarily a service provider interface (SPI), although it can be used programmatically

from your application code. Because PlatformTransactionManager is an interface, it can

be easily mocked or stubbed as necessary. It is not tied to a lookup strategy such as JNDI.

PlatformTransactionManager implementations are defined like any other object (or bean) in the

Spring Framework IoC container. This benefit alone makes Spring Framework transactions a worthwhile

abstraction even when you work with JTA. Transactional code can be tested much more easily than

if it used JTA directly.

Again in keeping with Spring’s philosophy, the TransactionException that can be thrown by any

of the PlatformTransactionManager interface’s methods is unchecked (that is, it extends the

java.lang.RuntimeException class). Transaction infrastructure failures are almost invariably fatal.

In rare cases where application code can actually recover from a transaction failure, the application

developer can still choose to catch and handle TransactionException. The salient point is that

developers are not forced to do so.

The getTransaction(..) method returns a TransactionStatus object, depending on a

TransactionDefinition parameter. The returned TransactionStatus might represent a new

transaction, or can represent an existing transaction if a matching transaction exists in the current

call stack. The implication in this latter case is that, as with Java EE transaction contexts, a

TransactionStatus is associated with a thread of execution.

The TransactionDefinition interface specifies:

•Isolation: The degree to which this transaction is isolated from the work of other transactions. For

example, can this transaction see uncommitted writes from other transactions?

•Propagation: Typically, all code executed within a transaction scope will run in that transaction.

However, you have the option of specifying the behavior in the event that a transactional method

is executed when a transaction context already exists. For example, code can continue running in

the existing transaction (the common case); or the existing transaction can be suspended and a new

transaction created. Spring offers all of the transaction propagation options familiar from EJB CMT.

To read about the semantics of transaction propagation in Spring, see the section called “Transaction

propagation”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 331

•Timeout: How long this transaction runs before timing out and being rolled back automatically by the

underlying transaction infrastructure.

•Read-only status: A read-only transaction can be used when your code reads but does not modify

data. Read-only transactions can be a useful optimization in some cases, such as when you are using

Hibernate.

These settings reflect standard transactional concepts. If necessary, refer to resources that discuss

transaction isolation levels and other core transaction concepts. Understanding these concepts is

essential to using the Spring Framework or any transaction management solution.

The TransactionStatus interface provides a simple way for transactional code to control transaction

execution and query transaction status. The concepts should be familiar, as they are common to all

transaction APIs:

public interface TransactionStatus extends SavepointManager {

boolean isNewTransaction();

boolean hasSavepoint();

void setRollbackOnly();

boolean isRollbackOnly();

void flush();

boolean isCompleted();

}

Regardless of whether you opt for declarative or programmatic transaction management in Spring,

defining the correct PlatformTransactionManager implementation is absolutely essential. You

typically define this implementation through dependency injection.

PlatformTransactionManager implementations normally require knowledge of the environment in

which they work: JDBC, JTA, Hibernate, and so on. The following examples show how you can define

a local PlatformTransactionManager implementation. (This example works with plain JDBC.)

You define a JDBC DataSource

</bean>

The related PlatformTransactionManager bean definition will then have a reference to the

DataSource definition. It will look like this:

</bean>

If you use JTA in a Java EE container then you use a container DataSource, obtained through JNDI,

in conjunction with Spring’s JtaTransactionManager. This is what the JTA and JNDI lookup version

would look like:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 332

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:jee="http://www.springframework.org/schema/jee"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/jee

http://www.springframework.org/schema/jee/spring-jee.xsd">

<jee:jndi-lookup id="dataSource" jndi-name="jdbc/jpetstore"/>

</beans>

The JtaTransactionManager does not need to know about the DataSource, or any other specific

resources, because it uses the container’s global transaction management infrastructure.

Note

The above definition of the dataSource bean uses the <jndi-lookup/> tag from the

jee namespace. For more information on schema-based configuration, see Chapter 34, XML

Schema-based configuration, and for more information on the <jee/> tags see the section

entitled the section called “the jee schema”.

You can also use Hibernate local transactions easily, as shown in the following examples. In this case,

you need to define a Hibernate LocalSessionFactoryBean, which your application code will use to

obtain Hibernate Session instances.

The DataSource bean definition will be similar to the local JDBC example shown previously and thus

is not shown in the following example.

Note

If the DataSource, used by any non-JTA transaction manager, is looked up via JNDI and

managed by a Java EE container, then it should be non-transactional because the Spring

Framework, rather than the Java EE container, will manage the transactions.

The txManager bean in this case is of the HibernateTransactionManager type. In the

same way as the DataSourceTransactionManager needs a reference to the DataSource, the

HibernateTransactionManager needs a reference to the SessionFactory.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 333

<list>

<value>org/springframework/samples/petclinic/hibernate/petclinic.hbm.xml</value>

</list>

</property>

<value>

hibernate.dialect=${hibernate.dialect}

</value>

</property>

</bean>

</bean>

If you are using Hibernate and Java EE container-managed JTA transactions, then you should simply

use the same JtaTransactionManager as in the previous JTA example for JDBC.

Note

If you use JTA , then your transaction manager definition will look the same regardless of what data

access technology you use, be it JDBC, Hibernate JPA or any other supported technology. This

is due to the fact that JTA transactions are global transactions, which can enlist any transactional

resource.

In all these cases, application code does not need to change. You can change how transactions are

managed merely by changing configuration, even if that change means moving from local to global

transactions or vice versa.

12.4 Synchronizing resources with transactions

It should now be clear how you create different transaction managers, and how they

are linked to related resources that need to be synchronized to transactions (for example

DataSourceTransactionManager to a JDBC DataSource, HibernateTransactionManager

to a Hibernate SessionFactory, and so forth). This section describes how the application code,

directly or indirectly using a persistence API such as JDBC, Hibernate, or JDO, ensures that these

resources are created, reused, and cleaned up properly. The section also discusses how transaction

synchronization is triggered (optionally) through the relevant PlatformTransactionManager.

High-level synchronization approach

The preferred approach is to use Spring’s highest level template based persistence integration APIs or to

use native ORM APIs with transaction- aware factory beans or proxies for managing the native resource

factories. These transaction-aware solutions internally handle resource creation and reuse, cleanup,

optional transaction synchronization of the resources, and exception mapping. Thus user data access

code does not have to address these tasks, but can be focused purely on non-boilerplate persistence

logic. Generally, you use the native ORM API or take a template approach for JDBC access by using the

JdbcTemplate. These solutions are detailed in subsequent chapters of this reference documentation.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 334

Low-level synchronization approach

Classes such as DataSourceUtils (for JDBC), EntityManagerFactoryUtils (for JPA),

SessionFactoryUtils (for Hibernate), PersistenceManagerFactoryUtils (for JDO), and so

on exist at a lower level. When you want the application code to deal directly with the resource types of

the native persistence APIs, you use these classes to ensure that proper Spring Framework-managed

instances are obtained, transactions are (optionally) synchronized, and exceptions that occur in the

process are properly mapped to a consistent API.

For example, in the case of JDBC, instead of the traditional JDBC approach of

calling the getConnection() method on the DataSource, you instead use Spring’s

org.springframework.jdbc.datasource.DataSourceUtils class as follows:

Connection conn = DataSourceUtils.getConnection(dataSource);

If an existing transaction already has a connection synchronized (linked) to it, that instance

is returned. Otherwise, the method call triggers the creation of a new connection, which is

(optionally) synchronized to any existing transaction, and made available for subsequent reuse

in that same transaction. As mentioned, any SQLException is wrapped in a Spring Framework

CannotGetJdbcConnectionException, one of the Spring Framework’s hierarchy of unchecked

DataAccessExceptions. This approach gives you more information than can be obtained easily from

the SQLException, and ensures portability across databases, even across different persistence

technologies.

This approach also works without Spring transaction management (transaction synchronization is

optional), so you can use it whether or not you are using Spring for transaction management.

Of course, once you have used Spring’s JDBC support, JPA support or Hibernate support, you will

generally prefer not to use DataSourceUtils or the other helper classes, because you will be much

happier working through the Spring abstraction than directly with the relevant APIs. For example, if

you use the Spring JdbcTemplate or jdbc.object package to simplify your use of JDBC, correct

connection retrieval occurs behind the scenes and you won’t need to write any special code.

TransactionAwareDataSourceProxy

At the very lowest level exists the TransactionAwareDataSourceProxy class. This is a proxy for

a target DataSource, which wraps the target DataSource to add awareness of Spring-managed

transactions. In this respect, it is similar to a transactional JNDI DataSource as provided by a Java

EE server.

It should almost never be necessary or desirable to use this class, except when existing code must be

called and passed a standard JDBC DataSource interface implementation. In that case, it is possible

that this code is usable, but participating in Spring managed transactions. It is preferable to write your

new code by using the higher level abstractions mentioned above.

12.5 Declarative transaction management

Note

Most Spring Framework users choose declarative transaction management. This option has the

least impact on application code, and hence is most consistent with the ideals of a non-invasive

lightweight container.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 335

The Spring Framework’s declarative transaction management is made possible with Spring aspect-

oriented programming (AOP), although, as the transactional aspects code comes with the Spring

Framework distribution and may be used in a boilerplate fashion, AOP concepts do not generally have

to be understood to make effective use of this code.

The Spring Framework’s declarative transaction management is similar to EJB CMT in that you can

specify transaction behavior (or lack of it) down to individual method level. It is possible to make a

setRollbackOnly() call within a transaction context if necessary. The differences between the two

types of transaction management are:

• Unlike EJB CMT, which is tied to JTA, the Spring Framework’s declarative transaction management

works in any environment. It can work with JTA transactions or local transactions using JDBC, JPA,

Hibernate or JDO by simply adjusting the configuration files.

• You can apply the Spring Framework declarative transaction management to any class, not merely

special classes such as EJBs.

• The Spring Framework offers declarative rollback rules,a feature with no EJB equivalent. Both

programmatic and declarative support for rollback rules is provided.

• The Spring Framework enables you to customize transactional behavior, by using AOP. For example,

you can insert custom behavior in the case of transaction rollback. You can also add arbitrary advice,

along with the transactional advice. With EJB CMT, you cannot influence the container’s transaction

management except with setRollbackOnly().

• The Spring Framework does not support propagation of transaction contexts across remote calls, as

do high-end application servers. If you need this feature, we recommend that you use EJB. However,

consider carefully before using such a feature, because normally, one does not want transactions to

span remote calls.

Where is TransactionProxyFactoryBean?

Declarative transaction configuration in versions of Spring 2.0 and above differs considerably from

previous versions of Spring. The main difference is that there is no longer any need to configure

TransactionProxyFactoryBean beans.

The pre-Spring 2.0 configuration style is still 100% valid configuration; think of the new <tx:tags/

> as simply defining TransactionProxyFactoryBean beans on your behalf.

The concept of rollback rules is important: they enable you to specify which exceptions (and throwables)

should cause automatic rollback. You specify this declaratively, in configuration, not in Java code. So,

although you can still call setRollbackOnly() on the TransactionStatus object to roll back the

current transaction back, most often you can specify a rule that MyApplicationException must

always result in rollback. The significant advantage to this option is that business objects do not depend

on the transaction infrastructure. For example, they typically do not need to import Spring transaction

APIs or other Spring APIs.

Although EJB container default behavior automatically rolls back the transaction on a system exception

(usually a runtime exception), EJB CMT does not roll back the transaction automatically on anapplication

exception (that is, a checked exception other than java.rmi.RemoteException). While the Spring

default behavior for declarative transaction management follows EJB convention (roll back is automatic

only on unchecked exceptions), it is often useful to customize this behavior.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 336

Understanding the Spring Framework’s declarative transaction

implementation

It is not sufficient to tell you simply to annotate your classes with the @Transactional annotation, add

@EnableTransactionManagement to your configuration, and then expect you to understand how it

all works. This section explains the inner workings of the Spring Framework’s declarative transaction

infrastructure in the event of transaction-related issues.

The most important concepts to grasp with regard to the Spring Framework’s declarative transaction

support are that this support is enabled via AOP proxies, and that the transactional advice is driven by

metadata (currently XML- or annotation-based). The combination of AOP with transactional metadata

yields an AOP proxy that uses a TransactionInterceptor in conjunction with an appropriate

PlatformTransactionManager implementation to drive transactions around method invocations.

Note

Spring AOP is covered in Chapter 9, Aspect Oriented Programming with Spring.

Conceptually, calling a method on a transactional proxy looks like this…

Figure 12.1.

Example of declarative transaction implementation

Consider the following interface, and its attendant implementation. This example uses Foo and Bar

classes as placeholders so that you can concentrate on the transaction usage without focusing on a

particular domain model. For the purposes of this example, the fact that the DefaultFooService

class throws UnsupportedOperationException instances in the body of each implemented

method is good; it allows you to see transactions created and then rolled back in response to the

UnsupportedOperationException instance.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 337

// the service interface that we want to make transactional

package x.y.service;

public interface FooService {

Foo getFoo(String fooName);

Foo getFoo(String fooName, String barName);

void insertFoo(Foo foo);

void updateFoo(Foo foo);

}

// an implementation of the above interface

package x.y.service;

public class DefaultFooService implements FooService {

public Foo getFoo(String fooName) {

throw new UnsupportedOperationException();

}

public Foo getFoo(String fooName, String barName) {

throw new UnsupportedOperationException();

}

public void insertFoo(Foo foo) {

throw new UnsupportedOperationException();

}

public void updateFoo(Foo foo) {

throw new UnsupportedOperationException();

}

Assume that the first two methods of the FooService interface, getFoo(String) and

getFoo(String, String), must execute in the context of a transaction with read-only semantics,

and that the other methods, insertFoo(Foo) and updateFoo(Foo), must execute in the context

of a transaction with read-write semantics. The following configuration is explained in detail in the next

few paragraphs.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 338

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<tx:advice id="txAdvice" transaction-manager="txManager">

<tx:attributes>

<tx:method name="get*" read-only="true"/>

<tx:method name=""/>

</tx:attributes>

</tx:advice>

<!-- ensure that the above transactional advice runs for any execution

of an operation defined by the FooService interface -->

<aop:config>

<aop:pointcut id="fooServiceOperation" expression="execution( x.y.service.FooService.*(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="fooServiceOperation"/>

</aop:config>

</bean>

</bean>

</beans>

Examine the preceding configuration. You want to make a service object, the fooService bean,

transactional. The transaction semantics to apply are encapsulated in the <tx:advice/> definition.

The <tx:advice/> definition reads as "… all methods on starting with 'get' are to execute in the

context of a read-only transaction, and all other methods are to execute with the default transaction

semantics". The transaction-manager attribute of the <tx:advice/> tag is set to the name of

the PlatformTransactionManager bean that is going to drive the transactions, in this case, the

txManager bean.

Tip

You can omit the transaction-manager attribute in the transactional advice ( <tx:advice/

>) if the bean name of the PlatformTransactionManager that you want to wire in has the

name transactionManager. If the PlatformTransactionManager bean that you want to

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 339

wire in has any other name, then you must use the transaction-manager attribute explicitly,

as in the preceding example.

The <aop:config/> definition ensures that the transactional advice defined by the txAdvice bean

executes at the appropriate points in the program. First you define a pointcut that matches the execution

of any operation defined in the FooService interface ( fooServiceOperation). Then you associate

the pointcut with the txAdvice using an advisor. The result indicates that at the execution of a

fooServiceOperation, the advice defined by txAdvice will be run.

The expression defined within the <aop:pointcut/> element is an AspectJ pointcut expression; see

Chapter 9, Aspect Oriented Programming with Spring for more details on pointcut expressions in Spring.

A common requirement is to make an entire service layer transactional. The best way to do this is simply

to change the pointcut expression to match any operation in your service layer. For example:

<aop:config>

<aop:pointcut id="fooServiceMethods" expression="execution(* x.y.service..(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="fooServiceMethods"/>

</aop:config>

Note

In this example it is assumed that all your service interfaces are defined in the x.y.service

package; see Chapter 9, Aspect Oriented Programming with Spring for more details.

Now that we’ve analyzed the configuration, you may be asking yourself, "Okay… but what does all this

configuration actually do?".

The above configuration will be used to create a transactional proxy around the object that is created

from the fooService bean definition. The proxy will be configured with the transactional advice, so that

when an appropriate method is invoked on the proxy, a transaction is started, suspended, marked as

read-only, and so on, depending on the transaction configuration associated with that method. Consider

the following program that test drives the above configuration:

public final class Boot {

public static void main(final String[] args) throws Exception {

ApplicationContext ctx = new ClassPathXmlApplicationContext("context.xml", Boot.class);

FooService fooService = (FooService) ctx.getBean("fooService");

fooService.insertFoo (new Foo());

}

The output from running the preceding program will resemble the following. (The Log4J output and

the stack trace from the UnsupportedOperationException thrown by the insertFoo(..) method of the

DefaultFooService class have been truncated for clarity.)

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 340

[AspectJInvocationContextExposingAdvisorAutoProxyCreator] - Creating implicit proxy for bean fooService

with 0 common interceptors and 1 specific interceptors

[JdkDynamicAopProxy] - Creating JDK dynamic proxy for [x.y.service.DefaultFooService]

[TransactionInterceptor] - Getting transaction for x.y.service.FooService.insertFoo

[DataSourceTransactionManager] - Creating new transaction with name [x.y.service.FooService.insertFoo]

[DataSourceTransactionManager] - Acquired Connection [org.apache.commons.dbcp.PoolableConnection@a53de4]

for JDBC transaction

[RuleBasedTransactionAttribute] - Applying rules to determine whether transaction should rollback on

java.lang.UnsupportedOperationException

[TransactionInterceptor] - Invoking rollback for transaction on x.y.service.FooService.insertFoo due to

throwable [java.lang.UnsupportedOperationException]

[DataSourceTransactionManager] - Rolling back JDBC transaction on Connection

[org.apache.commons.dbcp.PoolableConnection@a53de4]

[DataSourceTransactionManager] - Releasing JDBC Connection after transaction

[DataSourceUtils] - Returning JDBC Connection to DataSource

Exception in thread "main" java.lang.UnsupportedOperationException at

x.y.service.DefaultFooService.insertFoo(DefaultFooService.java:14)

at $Proxy0.insertFoo(Unknown Source)

at Boot.main(Boot.java:11)

Rolling back a declarative transaction

The previous section outlined the basics of how to specify transactional settings for classes, typically

service layer classes, declaratively in your application. This section describes how you can control the

rollback of transactions in a simple declarative fashion.

The recommended way to indicate to the Spring Framework’s transaction infrastructure that a

transaction’s work is to be rolled back is to throw an Exception from code that is currently executing

in the context of a transaction. The Spring Framework’s transaction infrastructure code will catch any

unhandled Exception as it bubbles up the call stack, and make a determination whether to mark the

transaction for rollback.

In its default configuration, the Spring Framework’s transaction infrastructure code only marks a

transaction for rollback in the case of runtime, unchecked exceptions; that is, when the thrown exception

is an instance or subclass of RuntimeException. ( Errors will also - by default - result in a rollback).

Checked exceptions that are thrown from a transactional method do not result in rollback in the default

configuration.

You can configure exactly which Exception types mark a transaction for rollback, including checked

exceptions. The following XML snippet demonstrates how you configure rollback for a checked,

application-specific Exception type.

<tx:advice id="txAdvice" transaction-manager="txManager">

<tx:attributes>

<tx:method name="get*" read-only="true" rollback-for="NoProductInStockException"/>

<tx:method name="*"/>

</tx:attributes>

</tx:advice>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 341

You can also specify no rollback rules, if you do not want a transaction rolled back when an exception

is thrown. The following example tells the Spring Framework’s transaction infrastructure to commit the

attendant transaction even in the face of an unhandled InstrumentNotFoundException.

<tx:advice id="txAdvice">

<tx:attributes>

<tx:method name="updateStock" no-rollback-for="InstrumentNotFoundException"/>

<tx:method name="*"/>

</tx:attributes>

</tx:advice>

When the Spring Framework’s transaction infrastructure catches an exception and is consults

configured rollback rules to determine whether to mark the transaction for rollback, the strongest

matching rule wins. So in the case of the following configuration, any exception other than an

InstrumentNotFoundException results in a rollback of the attendant transaction.

<tx:advice id="txAdvice">

<tx:attributes>

<tx:method name="*" rollback-for="Throwable" no-rollback-for="InstrumentNotFoundException"/>

</tx:attributes>

</tx:advice>

You can also indicate a required rollback programmatically. Although very simple, this process is quite

invasive, and tightly couples your code to the Spring Framework’s transaction infrastructure:

public void resolvePosition() {

try {

// some business logic...

} catch (NoProductInStockException ex) {

// trigger rollback programmatically

TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();

}

You are strongly encouraged to use the declarative approach to rollback if at all possible. Programmatic

rollback is available should you absolutely need it, but its usage flies in the face of achieving a clean

POJO-based architecture.

Configuring different transactional semantics for different beans

Consider the scenario where you have a number of service layer objects, and you want to apply a totally

different transactional configuration to each of them. You do this by defining distinct <aop:advisor/

> elements with differing pointcut and advice-ref attribute values.

As a point of comparison, first assume that all of your service layer classes are defined in a root

x.y.service package. To make all beans that are instances of classes defined in that package (or

in subpackages) and that have names ending in Service have the default transactional configuration,

you would write the following:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 342

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<aop:config>

<aop:pointcut id="serviceOperation"

expression="execution(* x.y.service..Service.(..))"/>

<aop:advisor pointcut-ref="serviceOperation" advice-ref="txAdvice"/>

</aop:config>

<tx:advice id="txAdvice">

<tx:attributes>

<tx:method name="get*" read-only="true"/>

<tx:method name="*"/>

</tx:attributes>

</tx:advice>

</beans>

The following example shows how to configure two distinct beans with totally different transactional

settings.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 343

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<aop:config>

<aop:pointcut id="defaultServiceOperation"

expression="execution(* x.y.service.Service.(..))"/>

<aop:pointcut id="noTxServiceOperation"

expression="execution(* x.y.service.ddl.DefaultDdlManager.(..))"/>

<aop:advisor pointcut-ref="defaultServiceOperation" advice-ref="defaultTxAdvice"/>

<aop:advisor pointcut-ref="noTxServiceOperation" advice-ref="noTxAdvice"/>

</aop:config>

<tx:advice id="defaultTxAdvice">

<tx:attributes>

<tx:method name="get" read-only="true"/>

<tx:method name=""/>

</tx:attributes>

</tx:advice>

<tx:advice id="noTxAdvice">

<tx:attributes>

<tx:method name="" propagation="NEVER"/>

</tx:attributes>

</tx:advice>

</beans>

<tx:advice/> settings

This section summarizes the various transactional settings that can be specified using the

<tx:advice/> tag. The default <tx:advice/> settings are:

•Propagation setting is REQUIRED.

• Isolation level is DEFAULT.

• Transaction is read/write.

• Transaction timeout defaults to the default timeout of the underlying transaction system, or none if

timeouts are not supported.

• Any RuntimeException triggers rollback, and any checked Exception does not.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 344

You can change these default settings; the various attributes of the <tx:method/> tags that are nested

within <tx:advice/> and <tx:attributes/> tags are summarized below:

Table 12.1. <tx:method/> settings

Attribute Required? Default Description

name Yes Method name(s) with

which the transaction

attributes are to

be associated.

The wildcard (*)

character can be

used to associate

the same transaction

attribute settings with

a number of methods;

for example, get*,

handle*, on*Event,

and so forth.

propagation No REQUIRED Transaction

propagation behavior.

isolation No DEFAULT Transaction isolation

level.

timeout No -1 Transaction timeout

value (in seconds).

read-only No false Is this transaction read-

only?

rollback-for No Exception(s)

that trigger rollback;

comma-delimited.

For example,

com.foo.MyBusinessException,ServletException.

no-rollback-for No Exception(s)

that do not trigger

rollback; comma-

delimited. For example,

com.foo.MyBusinessException,ServletException.

Using @Transactional

In addition to the XML-based declarative approach to transaction configuration, you can use an

annotation-based approach. Declaring transaction semantics directly in the Java source code puts the

declarations much closer to the affected code. There is not much danger of undue coupling, because

code that is meant to be used transactionally is almost always deployed that way anyway.

The ease-of-use afforded by the use of the @Transactional annotation is best illustrated with an

example, which is explained in the text that follows. Consider the following class definition:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 345

// the service class that we want to make transactional

@Transactional

public class DefaultFooService implements FooService {

Foo getFoo(String fooName);

Foo getFoo(String fooName, String barName);

void insertFoo(Foo foo);

void updateFoo(Foo foo);

}

When the above POJO is defined as a bean in a Spring IoC container, the bean instance can be made

transactional by adding merely one line of XML configuration:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<tx:annotation-driven transaction-manager="txManager"/><!-- a PlatformTransactionManager is still

required -->

</bean>

</beans>

Tip

You can omit the transaction-manager attribute in the <tx:annotation-driven/> tag

if the bean name of the PlatformTransactionManager that you want to wire in has the

name transactionManager. If the PlatformTransactionManager bean that you want to

dependency-inject has any other name, then you have to use the transaction-manager

attribute explicitly, as in the preceding example.

Note

The @EnableTransactionManagement annotation provides equivalent support if you are

using Java based configuration. Simply add the annotation to a @Configuration class. See

the javadocs for full details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 346

Method visibility and @Transactional

When using proxies, you should apply the @Transactional annotation only to methods

with public visibility. If you do annotate protected, private or package-visible methods with the

@Transactional annotation, no error is raised, but the annotated method does not exhibit the

configured transactional settings. Consider the use of AspectJ (see below) if you need to annotate

non-public methods.

You can place the @Transactional annotation before an interface definition, a method on an interface,

a class definition, or a public method on a class. However, the mere presence of the @Transactional

annotation is not enough to activate the transactional behavior. The @Transactional annotation is

simply metadata that can be consumed by some runtime infrastructure that is @Transactional-aware

and that can use the metadata to configure the appropriate beans with transactional behavior. In the

preceding example, the <tx:annotation-driven/> element switches on the transactional behavior.

Tip

Spring recommends that you only annotate concrete classes (and methods of concrete classes)

with the @Transactional annotation, as opposed to annotating interfaces. You certainly can

place the @Transactional annotation on an interface (or an interface method), but this works

only as you would expect it to if you are using interface-based proxies. The fact that Java

annotations are not inherited from interfaces means that if you are using class-based proxies (

proxy-target-class="true") or the weaving-based aspect ( mode="aspectj"), then the

transaction settings are not recognized by the proxying and weaving infrastructure, and the object

will not be wrapped in a transactional proxy, which would be decidedly bad.

Note

In proxy mode (which is the default), only external method calls coming in through the proxy are

intercepted. This means that self-invocation, in effect, a method within the target object calling

another method of the target object, will not lead to an actual transaction at runtime even if the

invoked method is marked with @Transactional.

Consider the use of AspectJ mode (see mode attribute in table below) if you expect self-invocations to

be wrapped with transactions as well. In this case, there will not be a proxy in the first place; instead,

the target class will be weaved (that is, its byte code will be modified) in order to turn @Transactional

into runtime behavior on any kind of method.

Table 12.2. Annotation driven transaction settings

XML Attribute Annotation Attribute Default Description

transaction-

manager

N/A (See

TransactionManagementConfigurer

javadocs)

transactionManager Name of transaction

manager to use. Only

required if the name

of the transaction

manager is not

transactionManager,

as in the example

above.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 347

XML Attribute Annotation Attribute Default Description

mode mode proxy The default mode

"proxy" processes

annotated beans

to be proxied using

Spring’s AOP

framework (following

proxy semantics, as

discussed above,

applying to method

calls coming in through

the proxy only). The

alternative mode

"aspectj" instead

weaves the affected

classes with Spring’s

AspectJ transaction

aspect, modifying the

target class byte code

to apply to any kind of

method call. AspectJ

weaving requires

spring-aspects.jar

in the classpath as

well as load-time

weaving (or compile-

time weaving) enabled.

(See the section called

“Spring configuration”

for details on how

to set up load-time

weaving.)

proxy-target-

class proxyTargetClass false Applies to proxy mode

only. Controls what

type of transactional

proxies are created for

classes annotated with

the @Transactional

annotation. If the

proxy-target-

class attribute is set

to true, then class-

based proxies are

created. If proxy-

target-class

is false or if the

attribute is omitted,

then standard JDK

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 348

XML Attribute Annotation Attribute Default Description

interface-based proxies

are created. (See

Section 9.6, “Proxying

mechanisms” for a

detailed examination

of the different proxy

types.)

order order Ordered.LOWEST_PRECEDENCEDefines the order

of the transaction

advice that is applied to

beans annotated with

@Transactional.

(For more information

about the rules related

to ordering of AOP

advice, see the

section called “Advice

ordering”.) No specified

ordering means that

the AOP subsystem

determines the order of

the advice.

Note

The proxy-target-class attribute controls what type of transactional proxies are created for

classes annotated with the @Transactional annotation. If proxy-target-class is set to

true, class-based proxies are created. If proxy-target-class is false or if the attribute

is omitted, standard JDK interface-based proxies are created. (See Section 9.6, “Proxying

mechanisms” for a discussion of the different proxy types.)

Note

@EnableTransactionManagement and <tx:annotation-driven/> only looks for

@Transactional on beans in the same application context they are defined in. This

means that, if you put annotation driven configuration in a WebApplicationContext for a

DispatcherServlet, it only checks for @Transactional beans in your controllers, and not

your services. See Section 17.2, “The DispatcherServlet” for more information.

The most derived location takes precedence when evaluating the transactional settings for a method. In

the case of the following example, the DefaultFooService class is annotated at the class level with

the settings for a read-only transaction, but the @Transactional annotation on the updateFoo(Foo)

method in the same class takes precedence over the transactional settings defined at the class level.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 349

@Transactional(readOnly = true)

public class DefaultFooService implements FooService {

public Foo getFoo(String fooName) {

// do something

}

// these settings have precedence for this method

@Transactional(readOnly = false, propagation = Propagation.REQUIRES_NEW)

public void updateFoo(Foo foo) {

// do something

}

@Transactional settings

The @Transactional annotation is metadata that specifies that an interface, class, or method must

have transactional semantics; for example, "start a brand new read-only transaction when this method

is invoked, suspending any existing transaction". The default @Transactional settings are as follows:

• Propagation setting is PROPAGATION_REQUIRED.

• Isolation level is ISOLATION_DEFAULT.

• Transaction is read/write.

• Transaction timeout defaults to the default timeout of the underlying transaction system, or to none

if timeouts are not supported.

• Any RuntimeException triggers rollback, and any checked Exception does not.

These default settings can be changed; the various properties of the @Transactional annotation are

summarized in the following table:

Table 12.3. @

Property Type Description

value String Optional qualifier specifying

the transaction manager to be

used.

propagation enum: Propagation Optional propagation setting.

isolation enum: Isolation Optional isolation level.

readOnly boolean Read/write vs. read-only

transaction

timeout int (in seconds granularity) Transaction timeout.

rollbackFor Array of Class objects,

which must be derived from

Throwable.

Optional array of exception

classes that must cause

rollback.

rollbackForClassName Array of class names.

Classes must be derived from

Throwable.

Optional array of names of

exception classes that must

cause rollback.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 350

Property Type Description

noRollbackFor Array of Class objects,

which must be derived from

Throwable.

Optional array of exception

classes that must not cause

rollback.

noRollbackForClassName Array of String class names,

which must be derived from

Throwable.

Optional array of names of

exception classes that must not

cause rollback.

Currently you cannot have explicit control over the name of a transaction, where name means the

transaction name that will be shown in a transaction monitor, if applicable (for example, WebLogic’s

transaction monitor), and in logging output. For declarative transactions, the transaction name is always

the fully-qualified class name + "." + method name of the transactionally-advised class. For example, if

the handlePayment(..) method of the BusinessService class started a transaction, the name of

the transaction would be: com.foo.BusinessService.handlePayment.

Multiple Transaction Managers with @Transactional

Most Spring applications only need a single transaction manager, but there may be situations

where you want multiple independent transaction managers in a single application. The value

attribute of the @Transactional annotation can be used to optionally specify the identity of the

PlatformTransactionManager to be used. This can either be the bean name or the qualifier value

of the transaction manager bean. For example, using the qualifier notation, the following Java code

public class TransactionalService {

@Transactional("order")

public void setSomething(String name) { ... }

@Transactional("account")

public void doSomething() { ... }

}

could be combined with the following transaction manager bean declarations in the application context.

<tx:annotation-driven/>

...

</bean>

...

</bean>

In this case, the two methods on TransactionalService will run under separate transaction

managers, differentiated by the "order" and "account" qualifiers. The default <tx:annotation-

driven> target bean name transactionManager will still be used if no specifically qualified

PlatformTransactionManager bean is found.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 351

Custom shortcut annotations

If you find you are repeatedly using the same attributes with @Transactional on many different

methods, then Spring’s meta-annotation support allows you to define custom shortcut annotations for

your specific use cases. For example, defining the following annotations

@Target({ElementType.METHOD, ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

@Transactional("order")

public @interface OrderTx {

}

@Target({ElementType.METHOD, ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

@Transactional("account")

public @interface AccountTx {

}

allows us to write the example from the previous section as

public class TransactionalService {

@OrderTx

public void setSomething(String name) { ... }

@AccountTx

public void doSomething() { ... }

}

Here we have used the syntax to define the transaction manager qualifier, but could also have included

propagation behavior, rollback rules, timeouts etc.

Transaction propagation

This section describes some semantics of transaction propagation in Spring. Please note that this

section is not an introduction to transaction propagation proper; rather it details some of the semantics

regarding transaction propagation in Spring.

In Spring-managed transactions, be aware of the difference between physical and logical transactions,

and how the propagation setting applies to this difference.

Required

Figure 12.2.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 352

PROPAGATION_REQUIRED

When the propagation setting is PROPAGATION_REQUIRED, a logical transaction scope is created for

each method upon which the setting is applied. Each such logical transaction scope can determine

rollback-only status individually, with an outer transaction scope being logically independent from the

inner transaction scope. Of course, in case of standard PROPAGATION_REQUIRED behavior, all these

scopes will be mapped to the same physical transaction. So a rollback-only marker set in the inner

transaction scope does affect the outer transaction’s chance to actually commit (as you would expect

it to).

However, in the case where an inner transaction scope sets the rollback-only marker, the outer

transaction has not decided on the rollback itself, and so the rollback (silently triggered by the inner

transaction scope) is unexpected. A corresponding UnexpectedRollbackException is thrown at

that point. This is expected behavior so that the caller of a transaction can never be misled to assume

that a commit was performed when it really was not. So if an inner transaction (of which the outer caller

is not aware) silently marks a transaction as rollback-only, the outer caller still calls commit. The outer

caller needs to receive an UnexpectedRollbackException to indicate clearly that a rollback was

performed instead.

RequiresNew

Figure 12.3.

PROPAGATION_REQUIRES_NEW

PROPAGATION_REQUIRES_NEW, in contrast to PROPAGATION_REQUIRED, uses a completely

independent transaction for each affected transaction scope. In that case, the underlying physical

transactions are different and hence can commit or roll back independently, with an outer transaction

not affected by an inner transaction’s rollback status.

Nested

PROPAGATION_NESTED uses a single physical transaction with multiple savepoints that it can roll back

to. Such partial rollbacks allow an inner transaction scope to trigger a rollback for its scope, with the

outer transaction being able to continue the physical transaction despite some operations having been

rolled back. This setting is typically mapped onto JDBC savepoints, so will only work with JDBC resource

transactions. See Spring’s DataSourceTransactionManager.

Advising transactional operations

Suppose you want to execute both transactional and some basic profiling advice. How do you effect

this in the context of <tx:annotation-driven/>?

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 353

When you invoke the updateFoo(Foo) method, you want to see the following actions:

• Configured profiling aspect starts up.

• Transactional advice executes.

• Method on the advised object executes.

• Transaction commits.

• Profiling aspect reports exact duration of the whole transactional method invocation.

Note

This chapter is not concerned with explaining AOP in any great detail (except as it applies to

transactions). See Chapter 9, Aspect Oriented Programming with Spring for detailed coverage of

the following AOP configuration and AOP in general.

Here is the code for a simple profiling aspect discussed above. The ordering of advice is controlled

through the Ordered interface. For full details on advice ordering, see the section called “Advice

ordering”. .

package x.y;

import org.aspectj.lang.ProceedingJoinPoint;

import org.springframework.util.StopWatch;

import org.springframework.core.Ordered;

public class SimpleProfiler implements Ordered {

private int order;

// allows us to control the ordering of advice

public int getOrder() {

return this.order;

}

public void setOrder(int order) {

this.order = order;

}

// this method is the around advice

public Object profile(ProceedingJoinPoint call) throws Throwable {

Object returnValue;

StopWatch clock = new StopWatch(getClass().getName());

try {

clock.start(call.toShortString());

returnValue = call.proceed();

} finally {

clock.stop();

System.out.println(clock.prettyPrint());

}

return returnValue;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 354

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

</bean>

<tx:annotation-driven transaction-manager="txManager" order="200"/>

<aop:config>

<aop:aspect id="profilingAspect" ref="profiler">

<aop:pointcut id="serviceMethodWithReturnValue"

expression="execution(!void x.y..Service.(..))"/>

<aop:around method="profile" pointcut-ref="serviceMethodWithReturnValue"/>

</aop:aspect>

</aop:config>

</bean>

</bean>

</beans>

The result of the above configuration is a fooService bean that has profiling and transactional aspects

applied to it in the desired order. You configure any number of additional aspects in similar fashion.

The following example effects the same setup as above, but uses the purely XML declarative approach.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 355

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

</bean>

<aop:config>

<aop:pointcut id="entryPointMethod" expression="execution(* x.y..Service.(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="entryPointMethod" order="2"/>

<aop:aspect id="profilingAspect" ref="profiler">

<aop:pointcut id="serviceMethodWithReturnValue"

expression="execution(!void x.y..Service.(..))"/>

<aop:around method="profile" pointcut-ref="serviceMethodWithReturnValue"/>

</aop:aspect>

</aop:config>

<tx:advice id="txAdvice" transaction-manager="txManager">

<tx:attributes>

<tx:method name="get*" read-only="true"/>

<tx:method name="*"/>

</tx:attributes>

</tx:advice>

</beans>

The result of the above configuration will be a fooService bean that has profiling and transactional

aspects applied to it in that order. If you want the profiling advice to execute after the transactional advice

on the way in, and before the transactional advice on the way out, then you simply swap the value of the

profiling aspect bean’s order property so that it is higher than the transactional advice’s order value.

You configure additional aspects in similar fashion.

Using @Transactional with AspectJ

It is also possible to use the Spring Framework’s @Transactional support outside of a Spring

container by means of an AspectJ aspect. To do so, you first annotate your classes (and optionally your

classes' methods) with the @Transactional annotation, and then you link (weave) your application

with the org.springframework.transaction.aspectj.AnnotationTransactionAspect

defined in the spring-aspects.jar file. The aspect must also be configured with a transaction

manager. You can of course use the Spring Framework’s IoC container to take care of dependency-

injecting the aspect. The simplest way to configure the transaction management aspect is to use the

<tx:annotation-driven/> element and specify the mode attribute to aspectj as described in the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 356

section called “Using @Transactional”. Because we’re focusing here on applications running outside of

a Spring container, we’ll show you how to do it programmatically.

Note

Prior to continuing, you may want to read the section called “Using @Transactional” and

Chapter 9, Aspect Oriented Programming with Spring respectively.

// construct an appropriate transaction manager

DataSourceTransactionManager txManager = new DataSourceTransactionManager(getDataSource());

// configure the AnnotationTransactionAspect to use it; this must be done before executing any

transactional methods

AnnotationTransactionAspect.aspectOf().setTransactionManager(txManager);

Note

When using this aspect, you must annotate the implementation class (and/or methods within

that class), not the interface (if any) that the class implements. AspectJ follows Java’s rule that

annotations on interfaces are not inherited.

The @Transactional annotation on a class specifies the default transaction semantics for the

execution of any method in the class.

The @Transactional annotation on a method within the class overrides the default transaction

semantics given by the class annotation (if present). Any method may be annotated, regardless of

visibility.

To weave your applications with the AnnotationTransactionAspect you must either build your

application with AspectJ (see the AspectJ Development Guide) or use load-time weaving. See the

section called “Load-time weaving with AspectJ in the Spring Framework” for a discussion of load-time

weaving with AspectJ.

12.6 Programmatic transaction management

The Spring Framework provides two means of programmatic transaction management:

• Using the TransactionTemplate.

• Using a PlatformTransactionManager implementation directly.

The Spring team generally recommends the TransactionTemplate for programmatic transaction

management. The second approach is similar to using the JTA UserTransaction API, although

exception handling is less cumbersome.

Using the TransactionTemplate

The TransactionTemplate adopts the same approach as other Spring templates such as the

JdbcTemplate. It uses a callback approach, to free application code from having to do the boilerplate

acquisition and release of transactional resources, and results in code that is intention driven, in that

the code that is written focuses solely on what the developer wants to do.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 357

Note

As you will see in the examples that follow, using the TransactionTemplate absolutely couples

you to Spring’s transaction infrastructure and APIs. Whether or not programmatic transaction

management is suitable for your development needs is a decision that you will have to make

yourself.

Application code that must execute in a transactional context, and that will use the

TransactionTemplate explicitly, looks like the following. You, as an application developer, write

a TransactionCallback implementation (typically expressed as an anonymous inner class) that

contains the code that you need to execute in the context of a transaction. You then pass an

instance of your custom TransactionCallback to the execute(..) method exposed on the

TransactionTemplate.

public class SimpleService implements Service {

// single TransactionTemplate shared amongst all methods in this instance

private final TransactionTemplate transactionTemplate;

// use constructor-injection to supply the PlatformTransactionManager

public SimpleService(PlatformTransactionManager transactionManager) {

Assert.notNull(transactionManager, "The transactionManager argument must not be null.");

this.transactionTemplate = new TransactionTemplate(transactionManager);

}

public Object someServiceMethod() {

return transactionTemplate.execute(new TransactionCallback() {

// the code in this method executes in a transactional context

public Object doInTransaction(TransactionStatus status) {

updateOperation1();

return resultOfUpdateOperation2();

}

});

}

If there is no return value, use the convenient TransactionCallbackWithoutResult class with an

anonymous class as follows:

transactionTemplate.execute(new TransactionCallbackWithoutResult() {

protected void doInTransactionWithoutResult(TransactionStatus status) {

updateOperation1();

updateOperation2();

}

});

Code within the callback can roll the transaction back by calling the setRollbackOnly() method on

the supplied TransactionStatus object:

transactionTemplate.execute(new TransactionCallbackWithoutResult() {

protected void doInTransactionWithoutResult(TransactionStatus status) {

try {

updateOperation1();

updateOperation2();

} catch (SomeBusinessExeption ex) {

status.setRollbackOnly();

}

});

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 358

Specifying transaction settings

You can specify transaction settings such as the propagation mode, the isolation level, the

timeout, and so forth on the TransactionTemplate either programmatically or in configuration.

TransactionTemplate instances by default have the default transactional settings. The following

example shows the programmatic customization of the transactional settings for a specific

TransactionTemplate:

public class SimpleService implements Service {

private final TransactionTemplate transactionTemplate;

public SimpleService(PlatformTransactionManager transactionManager) {

Assert.notNull(transactionManager, "The transactionManager argument must not be null.");

this.transactionTemplate = new TransactionTemplate(transactionManager);

// the transaction settings can be set here explicitly if so desired

this.transactionTemplate.setIsolationLevel(TransactionDefinition.ISOLATION_READ_UNCOMMITTED);

this.transactionTemplate.setTimeout(30); // 30 seconds

// and so forth...

}

The following example defines a TransactionTemplate with some custom transactional settings,

using Spring XML configuration. The sharedTransactionTemplate can then be injected into as

many services as are required.

<bean id="sharedTransactionTemplate"

class="org.springframework.transaction.support.TransactionTemplate">

</bean>"

Finally, instances of the TransactionTemplate class are threadsafe, in that instances do not maintain

any conversational state. TransactionTemplate instances do however maintain configuration state,

so while a number of classes may share a single instance of a TransactionTemplate, if a class

needs to use a TransactionTemplate with different settings (for example, a different isolation level),

then you need to create two distinct TransactionTemplate instances.

Using the PlatformTransactionManager

You can also use the org.springframework.transaction.PlatformTransactionManager

directly to manage your transaction. Simply pass the implementation of the

PlatformTransactionManager you are using to your bean through a bean reference. Then, using

the TransactionDefinition and TransactionStatus objects you can initiate transactions, roll

back, and commit.

DefaultTransactionDefinition def = new DefaultTransactionDefinition();

// explicitly setting the transaction name is something that can only be done programmatically

def.setName("SomeTxName");

def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);

TransactionStatus status = txManager.getTransaction(def);

try {

// execute your business logic here

}

catch (MyException ex) {

txManager.rollback(status);

throw ex;

}

txManager.commit(status);

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 359

12.7 Choosing between programmatic and declarative

transaction management

Programmatic transaction management is usually a good idea only if you have a small number of

transactional operations. For example, if you have a web application that require transactions only for

certain update operations, you may not want to set up transactional proxies using Spring or any other

technology. In this case, using the TransactionTemplate may be a good approach. Being able to

set the transaction name explicitly is also something that can only be done using the programmatic

approach to transaction management.

On the other hand, if your application has numerous transactional operations, declarative transaction

management is usually worthwhile. It keeps transaction management out of business logic, and is not

difficult to configure. When using the Spring Framework, rather than EJB CMT, the configuration cost

of declarative transaction management is greatly reduced.

12.8 Application server-specific integration

Spring’s transaction abstraction generally is application server agnostic. Additionally, Spring’s

JtaTransactionManager class, which can optionally perform a JNDI lookup for the JTA

UserTransaction and TransactionManager objects, autodetects the location for the latter

object, which varies by application server. Having access to the JTA TransactionManager

allows for enhanced transaction semantics, in particular supporting transaction suspension. See the

JtaTransactionManager javadocs for details.

Spring’s JtaTransactionManager is the standard choice to run on Java EE application servers,

and is known to work on all common servers. Advanced functionality such as transaction suspension

works on many servers as well — including GlassFish, JBoss and Geronimo — without any special

configuration required. However, for fully supported transaction suspension and further advanced

integration, Spring ships special adapters for WebLogic Server and WebSphere. These adapters are

discussed in the following sections.

For standard scenarios, including WebLogic Server and WebSphere, consider using the

convenient <tx:jta-transaction-manager/> configuration element. When configured, this

element automatically detects the underlying server and chooses the best transaction manager available

for the platform. This means that you won’t have to configure server-specific adapter classes (as

discussed in the following sections) explicitly; rather, they are chosen automatically, with the standard

JtaTransactionManager as default fallback.

IBM WebSphere

On WebSphere 6.1.0.9 and above, the recommended Spring JTA transaction manager to use

is WebSphereUowTransactionManager. This special adapter leverages IBM’s UOWManager

API, which is available in WebSphere Application Server 6.0.2.19 and later and 6.1.0.9 and

later. With this adapter, Spring-driven transaction suspension (suspend/resume as initiated by

PROPAGATION_REQUIRES_NEW) is officially supported by IBM!

Oracle WebLogic Server

On WebLogic Server 9.0 or above, you typically would use the WebLogicJtaTransactionManager

instead of the stock JtaTransactionManager class. This special WebLogic-specific subclass of

the normal JtaTransactionManager supports the full power of Spring’s transaction definitions in

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 360

a WebLogic-managed transaction environment, beyond standard JTA semantics: Features include

transaction names, per-transaction isolation levels, and proper resuming of transactions in all cases.

12.9 Solutions to common problems

Use of the wrong transaction manager for a specific DataSource

Use the correct PlatformTransactionManager implementation based on your choice of

transactional technologies and requirements. Used properly, the Spring Framework merely provides

a straightforward and portable abstraction. If you are using global transactions, you must use the

org.springframework.transaction.jta.JtaTransactionManager class (or an application

server-specific subclass of it) for all your transactional operations. Otherwise the transaction

infrastructure attempts to perform local transactions on resources such as container DataSource

instances. Such local transactions do not make sense, and a good application server treats them as

errors.

12.10 Further Resources

For more information about the Spring Framework’s transaction support:

•Distributed transactions in Spring, with and without XA is a JavaWorld presentation in which Spring’s

David Syer guides you through seven patterns for distributed transactions in Spring applications, three

of them with XA and four without.

•Java Transaction Design Strategies is a book available from InfoQ that provides a well-paced

introduction to transactions in Java. It also includes side-by-side examples of how to configure and

use transactions with both the Spring Framework and EJB3.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 361

13. DAO support

13.1 Introduction

The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access

technologies like JDBC, Hibernate, JPA or JDO in a consistent way. This allows one to switch between

the aforementioned persistence technologies fairly easily and it also allows one to code without worrying

about catching exceptions that are specific to each technology.

13.2 Consistent exception hierarchy

Spring provides a convenient translation from technology-specific exceptions like SQLException to

its own exception class hierarchy with the DataAccessException as the root exception. These

exceptions wrap the original exception so there is never any risk that one might lose any information

as to what might have gone wrong.

In addition to JDBC exceptions, Spring can also wrap Hibernate-specific exceptions, converting them

from proprietary, checked exceptions (in the case of versions of Hibernate prior to Hibernate 3.0), to a set

of focused runtime exceptions (the same is true for JDO and JPA exceptions). This allows one to handle

most persistence exceptions, which are non-recoverable, only in the appropriate layers, without having

annoying boilerplate catch-and-throw blocks and exception declarations in one’s DAOs. (One can still

trap and handle exceptions anywhere one needs to though.) As mentioned above, JDBC exceptions

(including database-specific dialects) are also converted to the same hierarchy, meaning that one can

perform some operations with JDBC within a consistent programming model.

The above holds true for the various template classes in Springs support for various

ORM frameworks. If one uses the interceptor-based classes then the application

must care about handling HibernateExceptions and JDOExceptions itself, preferably

via delegating to SessionFactoryUtils' convertHibernateAccessException(..) or

convertJdoAccessException() methods respectively. These methods convert the exceptions to

ones that are compatible with the exceptions in the org.springframework.dao exception hierarchy.

As JDOExceptions are unchecked, they can simply get thrown too, sacrificing generic DAO abstraction

in terms of exceptions though.

The exception hierarchy that Spring provides can be seen below. (Please note that the class hierarchy

detailed in the image shows only a subset of the entire DataAccessException hierarchy.)

Figure 13.1.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 362

13.3 Annotations used for configuring DAO or Repository

classes

The best way to guarantee that your Data Access Objects (DAOs) or repositories provide exception

translation is to use the @Repository annotation. This annotation also allows the component scanning

support to find and configure your DAOs and repositories without having to provide XML configuration

entries for them.

@Repository

public class SomeMovieFinder implements MovieFinder {

// ...

}

Any DAO or repository implementation will need to access to a persistence resource, depending on

the persistence technology used; for example, a JDBC-based repository will need access to a JDBC

DataSource; a JPA-based repository will need access to an EntityManager. The easiest way to

accomplish this is to have this resource dependency injected using one of the @Autowired,, @Inject,

@Resource or @PersistenceContext annotations. Here is an example for a JPA repository:

@Repository

public class JpaMovieFinder implements MovieFinder {

@PersistenceContext

private EntityManager entityManager;

// ...

}

If you are using the classic Hibernate APIs than you can inject the SessionFactory:

@Repository

public class HibernateMovieFinder implements MovieFinder {

private SessionFactory sessionFactory;

@Autowired

public void setSessionFactory(SessionFactory sessionFactory) {

this.sessionFactory = sessionFactory;

}

// ...

}

Last example we will show here is for typical JDBC support. You would have the DataSource injected

into an initialization method where you would create a JdbcTemplate and other data access support

classes like SimpleJdbcCall etc using this DataSource.

@Repository

public class JdbcMovieFinder implements MovieFinder {

private JdbcTemplate jdbcTemplate;

@Autowired

public void init(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 363

Note

Please see the specific coverage of each persistence technology for details on how to configure

the application context to take advantage of these annotations.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 364

14. Data access with JDBC

14.1 Introduction to Spring Framework JDBC

The value-add provided by the Spring Framework JDBC abstraction is perhaps best shown by the

sequence of actions outlined in the table below. The table shows what actions Spring will take care of

and which actions are the responsibility of you, the application developer.

Table 14.1. Spring JDBC - who does what?

Action Spring You

Define connection parameters. X

Open the connection. X

Specify the SQL statement. X

Declare parameters and

provide parameter values

Prepare and execute the

statement.

Set up the loop to iterate

through the results (if any).

Do the work for each iteration. X

Process any exception. X

Handle transactions. X

Close the connection,

statement and resultset.

The Spring Framework takes care of all the low-level details that can make JDBC such a tedious API

to develop with.

Choosing an approach for JDBC database access

You can choose among several approaches to form the basis for your JDBC database access. In

addition to three flavors of the JdbcTemplate, a new SimpleJdbcInsert and SimplejdbcCall approach

optimizes database metadata, and the RDBMS Object style takes a more object-oriented approach

similar to that of JDO Query design. Once you start using one of these approaches, you can still mix

and match to include a feature from a different approach. All approaches require a JDBC 2.0-compliant

driver, and some advanced features require a JDBC 3.0 driver.

•JdbcTemplate is the classic Spring JDBC approach and the most popular. This "lowest level"

approach and all others use a JdbcTemplate under the covers.

•NamedParameterJdbcTemplate wraps a JdbcTemplate to provide named parameters instead of

the traditional JDBC "?" placeholders. This approach provides better documentation and ease of use

when you have multiple parameters for an SQL statement.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 365

•SimpleJdbcInsert and SimpleJdbcCall optimize database metadata to limit the amount of necessary

configuration. This approach simplifies coding so that you only need to provide the name of the table

or procedure and provide a map of parameters matching the column names. This only works if the

database provides adequate metadata. If the database doesn’t provide this metadata, you will have

to provide explicit configuration of the parameters.

•RDBMS Objects including MappingSqlQuery, SqlUpdate and StoredProcedure requires you to create

reusable and thread-safe objects during initialization of your data access layer. This approach is

modeled after JDO Query wherein you define your query string, declare parameters, and compile

the query. Once you do that, execute methods can be called multiple times with various parameter

values passed in.

Package hierarchy

The Spring Framework’s JDBC abstraction framework consists of four different packages, namely core,

datasource, object, and support.

The org.springframework.jdbc.core package contains the JdbcTemplate

class and its various callback interfaces, plus a variety of

related classes. A subpackage named org.springframework.jdbc.core.simple

contains the SimpleJdbcInsert and SimpleJdbcCall classes. Another

subpackage named org.springframework.jdbc.core.namedparam contains the

NamedParameterJdbcTemplate class and the related support classes. See Section 14.2, “Using the

JDBC core classes to control basic JDBC processing and error handling”, Section 14.4, “JDBC batch

operations”, and Section 14.5, “Simplifying JDBC operations with the SimpleJdbc classes”

The org.springframework.jdbc.datasource package contains a utility class for easy

DataSource access, and various simple DataSource implementations that can be used for

testing and running unmodified JDBC code outside of a Java EE container. A subpackage named

org.springfamework.jdbc.datasource.embedded provides support for creating in-memory

database instances using Java database engines such as HSQL and H2. See Section 14.3, “Controlling

database connections” and Section 14.8, “Embedded database support”

The org.springframework.jdbc.object package contains classes that represent RDBMS

queries, updates, and stored procedures as thread safe, reusable objects. See Section 14.6, “Modeling

JDBC operations as Java objects”.This approach is modeled by JDO, although of course objects

returned by queries are "disconnected" from the database. This higher level of JDBC abstraction

depends on the lower-level abstraction in the org.springframework.jdbc.core package.

The org.springframework.jdbc.support package provides SQLException translation

functionality and some utility classes. Exceptions thrown during JDBC processing are translated to

exceptions defined in the org.springframework.dao package. This means that code using the

Spring JDBC abstraction layer does not need to implement JDBC or RDBMS-specific error handling.

All translated exceptions are unchecked, which gives you the option of catching the exceptions from

which you can recover while allowing other exceptions to be propagated to the caller. See the section

called “SQLExceptionTranslator”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 366

14.2 Using the JDBC core classes to control basic JDBC

processing and error handling

JdbcTemplate

The JdbcTemplate class is the central class in the JDBC core package. It handles the creation and

release of resources, which helps you avoid common errors such as forgetting to close the connection.

It performs the basic tasks of the core JDBC workflow such as statement creation and execution, leaving

application code to provide SQL and extract results. The JdbcTemplate class executes SQL queries,

update statements and stored procedure calls, performs iteration over ResultSets and extraction of

returned parameter values. It also catches JDBC exceptions and translates them to the generic, more

informative, exception hierarchy defined in the org.springframework.dao package.

When you use the JdbcTemplate for your code, you only need to implement callback interfaces,

giving them a clearly defined contract. The PreparedStatementCreator callback interface creates

a prepared statement given a Connection provided by this class, providing SQL and any necessary

parameters. The same is true for the CallableStatementCreator interface, which creates callable

statements. The RowCallbackHandler interface extracts values from each row of a ResultSet.

The JdbcTemplate can be used within a DAO implementation through direct instantiation with a

DataSource reference, or be configured in a Spring IoC container and given to DAOs as a bean

reference.

Note

The DataSource should always be configured as a bean in the Spring IoC container. In the

first case the bean is given to the service directly; in the second case it is given to the prepared

template.

All SQL issued by this class is logged at the DEBUG level under the category corresponding to the fully

qualified class name of the template instance (typically JdbcTemplate, but it may be different if you

are using a custom subclass of the JdbcTemplate class).

Examples of JdbcTemplate class usage

This section provides some examples of JdbcTemplate class usage. These examples are not an

exhaustive list of all of the functionality exposed by the JdbcTemplate; see the attendant javadocs

for that.

Querying (SELECT)

Here is a simple query for getting the number of rows in a relation:

int rowCount = this.jdbcTemplate.queryForObject("select count(*) from t_actor", Integer.class);

A simple query using a bind variable:

int countOfActorsNamedJoe = this.jdbcTemplate.queryForObject(

"select count(*) from t_actor where first_name = ?", Integer.class, "Joe");

Querying for a String:

String lastName = this.jdbcTemplate.queryForObject(

"select last_name from t_actor where id = ?",

new Object[]{1212L}, String.class);

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 367

Querying and populating a single domain object:

Actor actor = this.jdbcTemplate.queryForObject(

"select first_name, last_name from t_actor where id = ?",

new Object[]{1212L},

new RowMapper<Actor>() {

public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {

Actor actor = new Actor();

actor.setFirstName(rs.getString("first_name"));

actor.setLastName(rs.getString("last_name"));

return actor;

}

});

Querying and populating a number of domain objects:

List<Actor> actors = this.jdbcTemplate.query(

"select first_name, last_name from t_actor",

new RowMapper<Actor>() {

public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {

Actor actor = new Actor();

actor.setFirstName(rs.getString("first_name"));

actor.setLastName(rs.getString("last_name"));

return actor;

}

});

If the last two snippets of code actually existed in the same application, it would make sense to remove

the duplication present in the two RowMapper anonymous inner classes, and extract them out into a

single class (typically a static inner class) that can then be referenced by DAO methods as needed.

For example, it may be better to write the last code snippet as follows:

public List<Actor> findAllActors() {

return this.jdbcTemplate.query( "select first_name, last_name from t_actor", new ActorMapper());

}

private static final class ActorMapper implements RowMapper<Actor> {

public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {

Actor actor = new Actor();

actor.setFirstName(rs.getString("first_name"));

actor.setLastName(rs.getString("last_name"));

return actor;

}

Updating (INSERT/UPDATE/DELETE) with jdbcTemplate

You use the update(..) method to perform insert, update and delete operations. Parameter values

are usually provided as var args or alternatively as an object array.

this.jdbcTemplate.update(

"insert into t_actor (first_name, last_name) values (?, ?)",

"Leonor", "Watling");

this.jdbcTemplate.update(

"update t_actor set last_name = ? where id = ?",

"Banjo", 5276L);

this.jdbcTemplate.update(

"delete from actor where id = ?",

Long.valueOf(actorId));

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 368

Other jdbcTemplate operations

You can use the execute(..) method to execute any arbitrary SQL, and as such the method is

often used for DDL statements. It is heavily overloaded with variants taking callback interfaces, binding

variable arrays, and so on.

this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");

The following example invokes a simple stored procedure. More sophisticated stored procedure support

is covered later.

this.jdbcTemplate.update(

"call SUPPORT.REFRESH_ACTORS_SUMMARY(?)",

Long.valueOf(unionId));

JdbcTemplate best practices

Instances of the JdbcTemplate class are threadsafe once configured. This is important because it

means that you can configure a single instance of a JdbcTemplate and then safely inject this shared

reference into multiple DAOs (or repositories). The JdbcTemplate is stateful, in that it maintains a

reference to a DataSource, but this state is not conversational state.

A common practice when using the JdbcTemplate class (and the associated

NamedParameterJdbcTemplate classes) is to configure a DataSource in your Spring configuration

file, and then dependency-inject that shared DataSource bean into your DAO classes; the

JdbcTemplate is created in the setter for the DataSource. This leads to DAOs that look in part like

the following:

public class JdbcCorporateEventDao implements CorporateEventDao {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

// JDBC-backed implementations of the methods on the CorporateEventDao follow...

}

The corresponding configuration might look like this.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 369

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

</bean>

</bean>

<context:property-placeholder location="jdbc.properties"/>

</beans>

An alternative to explicit configuration is to use component-scanning and annotation support for

dependency injection. In this case you annotate the class with @Repository (which makes it a

candidate for component-scanning) and annotate the DataSource setter method with @Autowired.

@Repository

public class JdbcCorporateEventDao implements CorporateEventDao {

private JdbcTemplate jdbcTemplate;

@Autowired

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

// JDBC-backed implementations of the methods on the CorporateEventDao follow...

}

The corresponding XML configuration file would look like the following:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<!-- Scans within the base package of the application for @Component classes to configure as beans

-->

<context:component-scan base-package="org.springframework.docs.test" />

</bean>

<context:property-placeholder location="jdbc.properties"/>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 370

If you are using Spring’s JdbcDaoSupport class, and your various JDBC-backed DAO classes extend

from it, then your sub-class inherits a setDataSource(..) method from the JdbcDaoSupport class.

You can choose whether to inherit from this class. The JdbcDaoSupport class is provided as a

convenience only.

Regardless of which of the above template initialization styles you choose to use (or not), it is seldom

necessary to create a new instance of a JdbcTemplate class each time you want to execute SQL.

Once configured, a JdbcTemplate instance is threadsafe. You may want multiple JdbcTemplate

instances if your application accesses multiple databases, which requires multiple DataSources, and

subsequently multiple differently configured JdbcTemplates.

NamedParameterJdbcTemplate

The NamedParameterJdbcTemplate class adds support for programming JDBC statements using

named parameters, as opposed to programming JDBC statements using only classic placeholder (

'?') arguments. The NamedParameterJdbcTemplate class wraps a JdbcTemplate, and delegates

to the wrapped JdbcTemplate to do much of its work. This section describes only those areas

of the NamedParameterJdbcTemplate class that differ from the JdbcTemplate itself; namely,

programming JDBC statements using named parameters.

// some JDBC-backed DAO class...

private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);

}

public int countOfActorsByFirstName(String firstName) {

String sql = "select count(*) from T_ACTOR where first_name = :first_name";

SqlParameterSource namedParameters = new MapSqlParameterSource("first_name", firstName);

return this.namedParameterJdbcTemplate.queryForObject(sql, namedParameters, Integer.class);

}

Notice the use of the named parameter notation in the value assigned to the sql variable,

and the corresponding value that is plugged into the namedParameters variable (of type

MapSqlParameterSource).

Alternatively, you can pass along named parameters and their corresponding values to

a NamedParameterJdbcTemplate instance by using the Map-based style.The remaining

methods exposed by the NamedParameterJdbcOperations and implemented by the

NamedParameterJdbcTemplate class follow a similar pattern and are not covered here.

The following example shows the use of the Map-based style.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 371

// some JDBC-backed DAO class...

private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);

}

public int countOfActorsByFirstName(String firstName) {

String sql = "select count(*) from T_ACTOR where first_name = :first_name";

Map<String, String> namedParameters = Collections.singletonMap("first_name", firstName);

return this.namedParameterJdbcTemplate.queryForObject(sql, namedParameters, Integer.class);

}

One nice feature related to the NamedParameterJdbcTemplate (and existing in the

same Java package) is the SqlParameterSource interface. You have already seen an

example of an implementation of this interface in one of the previous code snippet (the

MapSqlParameterSource class). An SqlParameterSource is a source of named parameter

values to a NamedParameterJdbcTemplate. The MapSqlParameterSource class is a very simple

implementation that is simply an adapter around a java.util.Map, where the keys are the parameter

names and the values are the parameter values.

Another SqlParameterSource implementation is the BeanPropertySqlParameterSource class.

This class wraps an arbitrary JavaBean (that is, an instance of a class that adheres to the JavaBean

conventions), and uses the properties of the wrapped JavaBean as the source of named parameter

values.

public class Actor {

private Long id;

private String firstName;

private String lastName;

public String getFirstName() {

return this.firstName;

}

public String getLastName() {

return this.lastName;

}

public Long getId() {

return this.id;

}

// setters omitted...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 372

// some JDBC-backed DAO class...

private NamedParameterJdbcTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);

}

public int countOfActors(Actor exampleActor) {

// notice how the named parameters match the properties of the above Actor class

String sql = "select count(*) from T_ACTOR where first_name = :firstName and last_name = :lastName";

SqlParameterSource namedParameters = new BeanPropertySqlParameterSource(exampleActor);

return this.namedParameterJdbcTemplate.queryForObject(sql, namedParameters, Integer.class);

}

Remember that the NamedParameterJdbcTemplate class wraps a classic JdbcTemplate template;

if you need access to the wrapped JdbcTemplate instance to access functionality only present in

the JdbcTemplate class, you can use the getJdbcOperations() method to access the wrapped

JdbcTemplate through the JdbcOperations interface.

See also the section called “JdbcTemplate best practices” for guidelines on using the

NamedParameterJdbcTemplate class in the context of an application.

SQLExceptionTranslator

SQLExceptionTranslator is an interface to be implemented by classes that can translate between

SQLExceptions and Spring’s own org.springframework.dao.DataAccessException, which

is agnostic in regard to data access strategy. Implementations can be generic (for example, using

SQLState codes for JDBC) or proprietary (for example, using Oracle error codes) for greater precision.

SQLErrorCodeSQLExceptionTranslator is the implementation of SQLExceptionTranslator

that is used by default. This implementation uses specific vendor codes. It is more precise than the

SQLState implementation. The error code translations are based on codes held in a JavaBean type

class called SQLErrorCodes. This class is created and populated by an SQLErrorCodesFactory

which as the name suggests is a factory for creating SQLErrorCodes based on the contents of

a configuration file named sql-error-codes.xml. This file is populated with vendor codes and

based on the DatabaseProductName taken from the DatabaseMetaData. The codes for the actual

database you are using are used.

The SQLErrorCodeSQLExceptionTranslator applies matching rules in the following sequence:

Note

The SQLErrorCodesFactory is used by default to define Error codes and custom exception

translations. They are looked up in a file named sql-error-codes.xml from the classpath

and the matching SQLErrorCodes instance is located based on the database name from the

database metadata of the database in use.

• Any custom translation implemented by a subclass. Normally the provided concrete

SQLErrorCodeSQLExceptionTranslator is used so this rule does not apply. It only applies if

you have actually provided a subclass implementation.

• Any custom implementation of the SQLExceptionTranslator interface that is provided as the

customSqlExceptionTranslator property of the SQLErrorCodes class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 373

• The list of instances of the CustomSQLErrorCodesTranslation class, provided for the

customTranslations property of the SQLErrorCodes class, are searched for a match.

• Error code matching is applied.

• Use the fallback translator. SQLExceptionSubclassTranslator is the default fallback

translator. If this translation is not available then the next fallback translator is the

SQLStateSQLExceptionTranslator.

You can extend SQLErrorCodeSQLExceptionTranslator:

public class CustomSQLErrorCodesTranslator extends SQLErrorCodeSQLExceptionTranslator {

protected DataAccessException customTranslate(String task, String sql, SQLException sqlex) {

if (sqlex.getErrorCode() == -12345) {

return new DeadlockLoserDataAccessException(task, sqlex);

}

return null;

}

In this example, the specific error code -12345 is translated and other errors are left to be translated

by the default translator implementation. To use this custom translator, it is necessary to pass it to the

JdbcTemplate through the method setExceptionTranslator and to use this JdbcTemplate for

all of the data access processing where this translator is needed. Here is an example of how this custom

translator can be used:

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

// create a JdbcTemplate and set data source

this.jdbcTemplate = new JdbcTemplate();

this.jdbcTemplate.setDataSource(dataSource);

// create a custom translator and set the DataSource for the default translation lookup

CustomSQLErrorCodesTranslator tr = new CustomSQLErrorCodesTranslator();

tr.setDataSource(dataSource);

this.jdbcTemplate.setExceptionTranslator(tr);

}

public void updateShippingCharge(long orderId, long pct) {

// use the prepared JdbcTemplate for this update

this.jdbcTemplate.update("update orders" +

" set shipping_charge = shipping_charge * ? / 100" +

" where id = ?", pct, orderId);

}

The custom translator is passed a data source in order to look up the error codes in sql-error-

codes.xml.

Executing statements

Executing an SQL statement requires very little code. You need a DataSource and a JdbcTemplate,

including the convenience methods that are provided with the JdbcTemplate. The following example

shows what you need to include for a minimal but fully functional class that creates a new table:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 374

import javax.sql.DataSource;

import org.springframework.jdbc.core.JdbcTemplate;

public class ExecuteAStatement {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public void doExecute() {

this.jdbcTemplate.execute("create table mytable (id integer, name varchar(100))");

}

Running queries

Some query methods return a single value. To retrieve a count or a specific value from one row, use

queryForObject(..). The latter converts the returned JDBC Type to the Java class that is passed in

as an argument. If the type conversion is invalid, then an InvalidDataAccessApiUsageException

is thrown. Here is an example that contains two query methods, one for an int and one that queries

for a String.

import javax.sql.DataSource;

import org.springframework.jdbc.core.JdbcTemplate;

public class RunAQuery {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public int getCount() {

return this.jdbcTemplate.queryForObject("select count(*) from mytable", Integer.class);

}

public String getName() {

return this.jdbcTemplate.queryForObject("select name from mytable", String.class);

}

public void setDataSource(DataSource dataSource) {

this.dataSource = dataSource;

}

In addition to the single result query methods, several methods return a list with an entry for each row

that the query returned. The most generic method is queryForList(..) which returns a List where

each entry is a Map with each entry in the map representing the column value for that row. If you add a

method to the above example to retrieve a list of all the rows, it would look like this:

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public List<Map<String, Object>> getList() {

return this.jdbcTemplate.queryForList("select * from mytable");

}

The list returned would look something like this:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 375

[{name=Bob, id=1}, {name=Mary, id=2}]

Updating the database

The following example shows a column updated for a certain primary key. In this example, an SQL

statement has placeholders for row parameters. The parameter values can be passed in as varargs or

alternatively as an array of objects. Thus primitives should be wrapped in the primitive wrapper classes

explicitly or using auto-boxing.

import javax.sql.DataSource;

import org.springframework.jdbc.core.JdbcTemplate;

public class ExecuteAnUpdate {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public void setName(int id, String name) {

this.jdbcTemplate.update("update mytable set name = ? where id = ?", name, id);

}

Retrieving auto-generated keys

An update() convenience method supports the retrieval of primary keys generated by the database.

This support is part of the JDBC 3.0 standard; see Chapter 13.6 of the specification for details. The

method takes a PreparedStatementCreator as its first argument, and this is the way the required

insert statement is specified. The other argument is a KeyHolder, which contains the generated key

on successful return from the update. There is not a standard single way to create an appropriate

PreparedStatement (which explains why the method signature is the way it is). The following example

works on Oracle but may not work on other platforms:

final String INSERT_SQL = "insert into my_test (name) values(?)";

final String name = "Rob";

KeyHolder keyHolder = new GeneratedKeyHolder();

jdbcTemplate.update(

new PreparedStatementCreator() {

public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {

PreparedStatement ps = connection.prepareStatement(INSERT_SQL, new String[] {"id"});

ps.setString(1, name);

return ps;

}

keyHolder);

// keyHolder.getKey() now contains the generated key

14.3 Controlling database connections

DataSource

Spring obtains a connection to the database through a DataSource. A DataSource is part of the

JDBC specification and is a generalized connection factory. It allows a container or a framework to hide

connection pooling and transaction management issues from the application code. As a developer, you

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 376

need not know details about how to connect to the database; that is the responsibility of the administrator

that sets up the datasource. You most likely fill both roles as you develop and test code, but you do not

necessarily have to know how the production data source is configured.

When using Spring’s JDBC layer, you obtain a data source from JNDI or you configure your own

with a connection pool implementation provided by a third party. Popular implementations are Apache

Jakarta Commons DBCP and C3P0. Implementations in the Spring distribution are meant only for testing

purposes and do not provide pooling.

This section uses Spring’s DriverManagerDataSource implementation, and several additional

implementations are covered later.

Note

Only use the DriverManagerDataSource class should only be used for testing purposes since

it does not provide pooling and will perform poorly when multiple requests for a connection are

made.

You obtain a connection with DriverManagerDataSource as you typically obtain a JDBC connection.

Specify the fully qualified classname of the JDBC driver so that the DriverManager can load the driver

class. Next, provide a URL that varies between JDBC drivers. (Consult the documentation for your driver

for the correct value.) Then provide a username and a password to connect to the database. Here is an

example of how to configure a DriverManagerDataSource in Java code:

DriverManagerDataSource dataSource = new DriverManagerDataSource();

dataSource.setDriverClassName("org.hsqldb.jdbcDriver");

dataSource.setUrl("jdbc:hsqldb:hsql://localhost:");

dataSource.setUsername("sa");

dataSource.setPassword("");

Here is the corresponding XML configuration:

</bean>

<context:property-placeholder location="jdbc.properties"/>

The following examples show the basic connectivity and configuration for DBCP and C3P0. To learn

about more options that help control the pooling features, see the product documentation for the

respective connection pooling implementations.

DBCP configuration:

</bean>

<context:property-placeholder location="jdbc.properties"/>

C3P0 configuration:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 377

</bean>

<context:property-placeholder location="jdbc.properties"/>

DataSourceUtils

The DataSourceUtils class is a convenient and powerful helper class that provides static

methods to obtain connections from JNDI and close connections if necessary. It supports thread-bound

connections with, for example, DataSourceTransactionManager.

SmartDataSource

The SmartDataSource interface should be implemented by classes that can provide a connection to

a relational database. It extends the DataSource interface to allow classes using it to query whether

the connection should be closed after a given operation. This usage is efficient when you know that

you will reuse a connection.

AbstractDataSource

AbstractDataSource is an abstract base class for Spring’s DataSource implementations

that implements code that is common to all DataSource implementations. You extend the

AbstractDataSource class if you are writing your own DataSource implementation.

SingleConnectionDataSource

The SingleConnectionDataSource class is an implementation of the SmartDataSource interface

that wraps a single Connection that is not closed after each use. Obviously, this is not multi-threading

capable.

If any client code calls close in the assumption of a pooled connection, as when using persistence tools,

set the suppressClose property to true. This setting returns a close-suppressing proxy wrapping

the physical connection. Be aware that you will not be able to cast this to a native Oracle Connection

or the like anymore.

This is primarily a test class. For example, it enables easy testing of code outside an application server,

in conjunction with a simple JNDI environment. In contrast to DriverManagerDataSource, it reuses

the same connection all the time, avoiding excessive creation of physical connections.

DriverManagerDataSource

The DriverManagerDataSource class is an implementation of the standard DataSource interface

that configures a plain JDBC driver through bean properties, and returns a new Connection every time.

This implementation is useful for test and stand-alone environments outside of a Java EE container,

either as a DataSource bean in a Spring IoC container, or in conjunction with a simple JNDI

environment. Pool-assuming Connection.close() calls will simply close the connection, so any

DataSource-aware persistence code should work. However, using JavaBean-style connection pools

such as commons-dbcp is so easy, even in a test environment, that it is almost always preferable to

use such a connection pool over DriverManagerDataSource.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 378

TransactionAwareDataSourceProxy

TransactionAwareDataSourceProxy is a proxy for a target DataSource, which wraps that target

DataSource to add awareness of Spring-managed transactions. In this respect, it is similar to a

transactional JNDI DataSource as provided by a Java EE server.

Note

It is rarely desirable to use this class, except when already existing code that must be called

and passed a standard JDBC DataSource interface implementation. In this case, it’s possible

to still have this code be usable, and at the same time have this code participating in Spring

managed transactions. It is generally preferable to write your own new code using the higher level

abstractions for resource management, such as JdbcTemplate or DataSourceUtils.

(See the TransactionAwareDataSourceProxy javadocs for more details.)

DataSourceTransactionManager

The DataSourceTransactionManager class is a PlatformTransactionManager

implementation for single JDBC datasources. It binds a JDBC connection from the specified data source

to the currently executing thread, potentially allowing for one thread connection per data source.

Application code is required to retrieve the JDBC connection through

DataSourceUtils.getConnection(DataSource) instead of Java EE’s standard

DataSource.getConnection. It throws unchecked org.springframework.dao exceptions

instead of checked SQLExceptions. All framework classes like JdbcTemplate use this strategy

implicitly. If not used with this transaction manager, the lookup strategy behaves exactly like the common

one - it can thus be used in any case.

The DataSourceTransactionManager class supports custom isolation levels, and timeouts that

get applied as appropriate JDBC statement query timeouts. To support the latter, application code

must either use JdbcTemplate or call the DataSourceUtils.applyTransactionTimeout(..)

method for each created statement.

This implementation can be used instead of JtaTransactionManager in the single resource case, as

it does not require the container to support JTA. Switching between both is just a matter of configuration,

if you stick to the required connection lookup pattern. JTA does not support custom isolation levels!

NativeJdbcExtractor

Sometimes you need to access vendor specific JDBC methods that differ from the standard JDBC

API. This can be problematic if you are running in an application server or with a DataSource that

wraps the Connection, Statement and ResultSet objects with its own wrapper objects. To gain

access to the native objects you can configure your JdbcTemplate or OracleLobHandler with a

NativeJdbcExtractor.

The NativeJdbcExtractor comes in a variety of flavors to match your execution environment:

• SimpleNativeJdbcExtractor

• C3P0NativeJdbcExtractor

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 379

• CommonsDbcpNativeJdbcExtractor

• JBossNativeJdbcExtractor

• WebLogicNativeJdbcExtractor

• WebSphereNativeJdbcExtractor

• XAPoolNativeJdbcExtractor

Usually the SimpleNativeJdbcExtractor is sufficient for unwrapping a Connection object in most

environments. See the javadocs for more details.

14.4 JDBC batch operations

Most JDBC drivers provide improved performance if you batch multiple calls to the same prepared

statement. By grouping updates into batches you limit the number of round trips to the database.

Basic batch operations with the JdbcTemplate

You accomplish JdbcTemplate batch processing by implementing two methods of a special

interface, BatchPreparedStatementSetter, and passing that in as the second parameter in your

batchUpdate method call. Use the getBatchSize method to provide the size of the current batch.

Use the setValues method to set the values for the parameters of the prepared statement. This method

will be called the number of times that you specified in the getBatchSize call. The following example

updates the actor table based on entries in a list. The entire list is used as the batch in this example:

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public int[] batchUpdate(final List<Actor> actors) {

int[] updateCounts = jdbcTemplate.batchUpdate("update t_actor set first_name = ?, " +

"last_name = ? where id = ?",

new BatchPreparedStatementSetter() {

public void setValues(PreparedStatement ps, int i) throws SQLException {

ps.setString(1, actors.get(i).getFirstName());

ps.setString(2, actors.get(i).getLastName());

ps.setLong(3, actors.get(i).getId().longValue());

}

public int getBatchSize() {

return actors.size();

}

});

return updateCounts;

}

// ... additional methods

}

If you are processing a stream of updates or reading from a file, then you might have a preferred

batch size, but the last batch might not have that number of entries. In this case you can use the

InterruptibleBatchPreparedStatementSetter interface, which allows you to interrupt a batch

once the input source is exhausted. The isBatchExhausted method allows you to signal the end of

the batch.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 380

Batch operations with a List of objects

Both the JdbcTemplate and the NamedParameterJdbcTemplate provides an alternate way of

providing the batch update. Instead of implementing a special batch interface, you provide all parameter

values in the call as a list. The framework loops over these values and uses an internal prepared

statement setter. The API varies depending on whether you use named parameters. For the named

parameters you provide an array of SqlParameterSource, one entry for each member of the batch.

You can use the SqlParameterSource.createBatch method to create this array, passing in either

an array of JavaBeans or an array of Maps containing the parameter values.

This example shows a batch update using named parameters:

public class JdbcActorDao implements ActorDao {

private NamedParameterTemplate namedParameterJdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);

}

public int[] batchUpdate(final List<Actor> actors) {

SqlParameterSource[] batch = SqlParameterSourceUtils.createBatch(actors.toArray());

int[] updateCounts = namedParameterJdbcTemplate.batchUpdate(

"update t_actor set first_name = :firstName, last_name = :lastName where id = :id",

batch);

return updateCounts;

}

// ... additional methods

}

For an SQL statement using the classic "?" placeholders, you pass in a list containing an object array

with the update values. This object array must have one entry for each placeholder in the SQL statement,

and they must be in the same order as they are defined in the SQL statement.

The same example using classic JDBC "?" placeholders:

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public int[] batchUpdate(final List<Actor> actors) {

List<Object[]> batch = new ArrayList<Object[]>();

for (Actor actor : actors) {

Object[] values = new Object[] {

actor.getFirstName(),

actor.getLastName(),

actor.getId()};

batch.add(values);

}

int[] updateCounts = jdbcTemplate.batchUpdate(

"update t_actor set first_name = ?, last_name = ? where id = ?",

batch);

return updateCounts;

}

// ... additional methods

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 381

All of the above batch update methods return an int array containing the number of affected rows for

each batch entry. This count is reported by the JDBC driver. If the count is not available, the JDBC

driver returns a -2 value.

Batch operations with multiple batches

The last example of a batch update deals with batches that are so large that you want to break them up

into several smaller batches. You can of course do this with the methods mentioned above by making

multiple calls to the batchUpdate method, but there is now a more convenient method. This method

takes, in addition to the SQL statement, a Collection of objects containing the parameters, the number

of updates to make for each batch and a ParameterizedPreparedStatementSetter to set the

values for the parameters of the prepared statement. The framework loops over the provided values

and breaks the update calls into batches of the size specified.

This example shows a batch update using a batch size of 100:

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

}

public int[][] batchUpdate(final Collection<Actor> actors) {

int[][] updateCounts = jdbcTemplate.batchUpdate(

"update t_actor set first_name = ?, last_name = ? where id = ?",

actors,

100,

new ParameterizedPreparedStatementSetter<Actor>() {

public void setValues(PreparedStatement ps, Actor argument) throws SQLException {

ps.setString(1, argument.getFirstName());

ps.setString(2, argument.getLastName());

ps.setLong(3, argument.getId().longValue());

}

});

return updateCounts;

}

// ... additional methods

}

The batch update methods for this call returns an array of int arrays containing an array entry for each

batch with an array of the number of affected rows for each update. The top level array’s length indicates

the number of batches executed and the second level array’s length indicates the number of updates in

that batch. The number of updates in each batch should be the the batch size provided for all batches

except for the last one that might be less, depending on the total number of update objects provided.

The update count for each update statement is the one reported by the JDBC driver. If the count is not

available, the JDBC driver returns a -2 value.

14.5 Simplifying JDBC operations with the SimpleJdbc classes

The SimpleJdbcInsert and SimpleJdbcCall classes provide a simplified configuration by taking

advantage of database metadata that can be retrieved through the JDBC driver. This means there is

less to configure up front, although you can override or turn off the metadata processing if you prefer

to provide all the details in your code.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 382

Inserting data using SimpleJdbcInsert

Let’s start by looking at the SimpleJdbcInsert class with the minimal amount of configuration options.

You should instantiate the SimpleJdbcInsert in the data access layer’s initialization method. For

this example, the initializing method is the setDataSource method. You do not need to subclass

the SimpleJdbcInsert class; simply create a new instance and set the table name using the

withTableName method. Configuration methods for this class follow the "fluid" style that returns the

instance of the SimpleJdbcInsert, which allows you to chain all configuration methods. This example

uses only one configuration method; you will see examples of multiple ones later.

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcInsert insertActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.insertActor = new SimpleJdbcInsert(dataSource).withTableName("t_actor");

}

public void add(Actor actor) {

Map<String, Object> parameters = new HashMap<String, Object>(3);

parameters.put("id", actor.getId());

parameters.put("first_name", actor.getFirstName());

parameters.put("last_name", actor.getLastName());

insertActor.execute(parameters);

}

// ... additional methods

}

The execute method used here takes a plain java.utils.Map as its only parameter. The important

thing to note here is that the keys used for the Map must match the column names of the table as defined

in the database. This is because we read the metadata in order to construct the actual insert statement.

Retrieving auto-generated keys using SimpleJdbcInsert

This example uses the same insert as the preceding, but instead of passing in the id it retrieves the

auto-generated key and sets it on the new Actor object. When you create the SimpleJdbcInsert,

in addition to specifying the table name, you specify the name of the generated key column with the

usingGeneratedKeyColumns method.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 383

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcInsert insertActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.insertActor = new SimpleJdbcInsert(dataSource)

.withTableName("t_actor")

.usingGeneratedKeyColumns("id");

}

public void add(Actor actor) {

Map<String, Object> parameters = new HashMap<String, Object>(2);

parameters.put("first_name", actor.getFirstName());

parameters.put("last_name", actor.getLastName());

Number newId = insertActor.executeAndReturnKey(parameters);

actor.setId(newId.longValue());

}

// ... additional methods

}

The main difference when executing the insert by this second approach is that you do not add the id to

the Map and you call the executeReturningKey method. This returns a java.lang.Number object

with which you can create an instance of the numerical type that is used in our domain class. You cannot

rely on all databases to return a specific Java class here; java.lang.Number is the base class that

you can rely on. If you have multiple auto-generated columns, or the generated values are non-numeric,

then you can use a KeyHolder that is returned from the executeReturningKeyHolder method.

Specifying columns for a SimpleJdbcInsert

You can limit the columns for an insert by specifying a list of column names with the usingColumns

method:

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcInsert insertActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.insertActor = new SimpleJdbcInsert(dataSource)

.withTableName("t_actor")

.usingColumns("first_name", "last_name")

.usingGeneratedKeyColumns("id");

}

public void add(Actor actor) {

Map<String, Object> parameters = new HashMap<String, Object>(2);

parameters.put("first_name", actor.getFirstName());

parameters.put("last_name", actor.getLastName());

Number newId = insertActor.executeAndReturnKey(parameters);

actor.setId(newId.longValue());

}

// ... additional methods

}

The execution of the insert is the same as if you had relied on the metadata to determine which columns

to use.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 384

Using SqlParameterSource to provide parameter values

Using a Map to provide parameter values works fine, but it’s not the most convenient class to use.

Spring provides a couple of implementations of the SqlParameterSource interface that can be used

instead.The first one is BeanPropertySqlParameterSource, which is a very convenient class if you

have a JavaBean-compliant class that contains your values. It will use the corresponding getter method

to extract the parameter values. Here is an example:

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcInsert insertActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.insertActor = new SimpleJdbcInsert(dataSource)

.withTableName("t_actor")

.usingGeneratedKeyColumns("id");

}

public void add(Actor actor) {

SqlParameterSource parameters = new BeanPropertySqlParameterSource(actor);

Number newId = insertActor.executeAndReturnKey(parameters);

actor.setId(newId.longValue());

}

// ... additional methods

}

Another option is the MapSqlParameterSource that resembles a Map but provides a more convenient

addValue method that can be chained.

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcInsert insertActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.insertActor = new SimpleJdbcInsert(dataSource)

.withTableName("t_actor")

.usingGeneratedKeyColumns("id");

}

public void add(Actor actor) {

SqlParameterSource parameters = new MapSqlParameterSource()

.addValue("first_name", actor.getFirstName())

.addValue("last_name", actor.getLastName());

Number newId = insertActor.executeAndReturnKey(parameters);

actor.setId(newId.longValue());

}

// ... additional methods

}

As you can see, the configuration is the same; only the executing code has to change to use these

alternative input classes.

Calling a stored procedure with SimpleJdbcCall

The SimpleJdbcCall class leverages metadata in the database to look up names of in and out

parameters, so that you do not have to declare them explicitly. You can declare parameters if you prefer

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 385

to do that, or if you have parameters such as ARRAY or STRUCT that do not have an automatic mapping

to a Java class. The first example shows a simple procedure that returns only scalar values in VARCHAR

and DATE format from a MySQL database. The example procedure reads a specified actor entry and

returns first_name, last_name, and birth_date columns in the form of out parameters.

CREATE PROCEDURE read_actor (

IN in_id INTEGER,

OUT out_first_name VARCHAR(100),

OUT out_last_name VARCHAR(100),

OUT out_birth_date DATE)

BEGIN

SELECT first_name, last_name, birth_date

INTO out_first_name, out_last_name, out_birth_date

FROM t_actor where id = in_id;

END;

The in_id parameter contains the id of the actor you are looking up. The out parameters return the

data read from the table.

The SimpleJdbcCall is declared in a similar manner to the SimpleJdbcInsert. You should

instantiate and configure the class in the initialization method of your data access layer. Compared to the

StoredProcedure class, you don’t have to create a subclass and you don’t have to declare parameters

that can be looked up in the database metadata. Following is an example of a SimpleJdbcCall

configuration using the above stored procedure. The only configuration option, in addition to the

DataSource, is the name of the stored procedure.

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcCall procReadActor;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

this.procReadActor = new SimpleJdbcCall(dataSource)

.withProcedureName("read_actor");

}

public Actor readActor(Long id) {

SqlParameterSource in = new MapSqlParameterSource()

.addValue("in_id", id);

Map out = procReadActor.execute(in);

Actor actor = new Actor();

actor.setId(id);

actor.setFirstName((String) out.get("out_first_name"));

actor.setLastName((String) out.get("out_last_name"));

actor.setBirthDate((Date) out.get("out_birth_date"));

return actor;

}

// ... additional methods

}

The code you write for the execution of the call involves creating an SqlParameterSource containing

the IN parameter. It’s important to match the name provided for the input value with that of the parameter

name declared in the stored procedure. The case does not have to match because you use metadata

to determine how database objects should be referred to in a stored procedure. What is specified in the

source for the stored procedure is not necessarily the way it is stored in the database. Some databases

transform names to all upper case while others use lower case or use the case as specified.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 386

The execute method takes the IN parameters and returns a Map containing any out parameters

keyed by the name as specified in the stored procedure. In this case they are out_first_name,

out_last_name and out_birth_date.

The last part of the execute method creates an Actor instance to use to return the data retrieved.

Again, it is important to use the names of the out parameters as they are declared in the stored

procedure. Also, the case in the names of the out parameters stored in the results map matches

that of the out parameter names in the database, which could vary between databases. To make

your code more portable you should do a case-insensitive lookup or instruct Spring to use a

CaseInsensitiveMap from the Jakarta Commons project. To do the latter, you create your own

JdbcTemplate and set the setResultsMapCaseInsensitive property to true. Then you pass

this customized JdbcTemplate instance into the constructor of your SimpleJdbcCall. You must

include the commons-collections.jar in your classpath for this to work. Here is an example of this

configuration:

public class JdbcActorDao implements ActorDao {

private SimpleJdbcCall procReadActor;

public void setDataSource(DataSource dataSource) {

JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

jdbcTemplate.setResultsMapCaseInsensitive(true);

this.procReadActor = new SimpleJdbcCall(jdbcTemplate)

.withProcedureName("read_actor");

}

// ... additional methods

}

By taking this action, you avoid conflicts in the case used for the names of your returned out parameters.

Explicitly declaring parameters to use for a SimpleJdbcCall

You have seen how the parameters are deduced based on metadata, but you can declare then explicitly

if you wish. You do this by creating and configuring SimpleJdbcCall with the declareParameters

method, which takes a variable number of SqlParameter objects as input. See the next section for

details on how to define an SqlParameter.

Note

Explicit declarations are necessary if the database you use is not a Spring-supported database.

Currently Spring supports metadata lookup of stored procedure calls for the following databases:

Apache Derby, DB2, MySQL, Microsoft SQL Server, Oracle, and Sybase. We also support

metadata lookup of stored functions for: MySQL, Microsoft SQL Server, and Oracle.

You can opt to declare one, some, or all the parameters explicitly. The parameter metadata is

still used where you do not declare parameters explicitly. To bypass all processing of metadata

lookups for potential parameters and only use the declared parameters, you call the method

withoutProcedureColumnMetaDataAccess as part of the declaration. Suppose that you have

two or more different call signatures declared for a database function. In this case you call the

useInParameterNames to specify the list of IN parameter names to include for a given signature.

The following example shows a fully declared procedure call, using the information from the preceding

example.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 387

public class JdbcActorDao implements ActorDao {

private SimpleJdbcCall procReadActor;

public void setDataSource(DataSource dataSource) {

JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

jdbcTemplate.setResultsMapCaseInsensitive(true);

this.procReadActor = new SimpleJdbcCall(jdbcTemplate)

.withProcedureName("read_actor")

.withoutProcedureColumnMetaDataAccess()

.useInParameterNames("in_id")

.declareParameters(

new SqlParameter("in_id", Types.NUMERIC),

new SqlOutParameter("out_first_name", Types.VARCHAR),

new SqlOutParameter("out_last_name", Types.VARCHAR),

new SqlOutParameter("out_birth_date", Types.DATE)

);

}

// ... additional methods

}

The execution and end results of the two examples are the same; this one specifies all details explicitly

rather than relying on metadata.

How to define SqlParameters

To define a parameter for the SimpleJdbc classes and also for the RDBMS operations classes, covered

in Section 14.6, “Modeling JDBC operations as Java objects”, you use an SqlParameter or one of its

subclasses. You typically specify the parameter name and SQL type in the constructor. The SQL type

is specified using the java.sql.Types constants. We have already seen declarations like:

new SqlParameter("in_id", Types.NUMERIC),

new SqlOutParameter("out_first_name", Types.VARCHAR),

The first line with the SqlParameter declares an IN parameter. IN parameters can be used for both

stored procedure calls and for queries using the SqlQuery and its subclasses covered in the following

section.

The second line with the SqlOutParameter declares an out parameter to be used in a stored

procedure call. There is also an SqlInOutParameter for InOut parameters, parameters that provide

an IN value to the procedure and that also return a value.

Note

Only parameters declared as SqlParameter and SqlInOutParameter will be used

to provide input values. This is different from the StoredProcedure class, which for

backwards compatibility reasons allows input values to be provided for parameters declared as

SqlOutParameter.

For IN parameters, in addition to the name and the SQL type, you can specify a scale for numeric data

or a type name for custom database types. For out parameters, you can provide a RowMapper to

handle mapping of rows returned from a REF cursor. Another option is to specify an SqlReturnType

that provides an opportunity to define customized handling of the return values.

Calling a stored function using SimpleJdbcCall

You call a stored function in almost the same way as you call a stored procedure, except that you

provide a function name rather than a procedure name. You use the withFunctionName method as

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 388

part of the configuration to indicate that we want to make a call to a function, and the corresponding

string for a function call is generated. A specialized execute call, executeFunction, is used to

execute the function and it returns the function return value as an object of a specified type, which

means you do not have to retrieve the return value from the results map. A similar convenience method

named executeObject is also available for stored procedures that only have one out parameter. The

following example is based on a stored function named get_actor_name that returns an actor’s full

name. Here is the MySQL source for this function:

CREATE FUNCTION get_actor_name (in_id INTEGER)

RETURNS VARCHAR(200) READS SQL DATA

BEGIN

DECLARE out_name VARCHAR(200);

SELECT concat(first_name, ' ', last_name)

INTO out_name

FROM t_actor where id = in_id;

RETURN out_name;

END;

To call this function we again create a SimpleJdbcCall in the initialization method.

public class JdbcActorDao implements ActorDao {

private JdbcTemplate jdbcTemplate;

private SimpleJdbcCall funcGetActorName;

public void setDataSource(DataSource dataSource) {

this.jdbcTemplate = new JdbcTemplate(dataSource);

JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

jdbcTemplate.setResultsMapCaseInsensitive(true);

this.funcGetActorName = new SimpleJdbcCall(jdbcTemplate)

.withFunctionName("get_actor_name");

}

public String getActorName(Long id) {

SqlParameterSource in = new MapSqlParameterSource()

.addValue("in_id", id);

String name = funcGetActorName.executeFunction(String.class, in);

return name;

}

// ... additional methods

}

The execute method used returns a String containing the return value from the function call.

Returning ResultSet/REF Cursor from a SimpleJdbcCall

Calling a stored procedure or function that returns a result set is a bit tricky. Some databases return result

sets during the JDBC results processing while others require an explicitly registered out parameter of

a specific type. Both approaches need additional processing to loop over the result set and process the

returned rows. With the SimpleJdbcCall you use the returningResultSet method and declare

a RowMapper implementation to be used for a specific parameter. In the case where the result set is

returned during the results processing, there are no names defined, so the returned results will have to

match the order in which you declare the RowMapper implementations. The name specified is still used

to store the processed list of results in the results map that is returned from the execute statement.

The next example uses a stored procedure that takes no IN parameters and returns all rows from the

t_actor table. Here is the MySQL source for this procedure:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 389

CREATE PROCEDURE read_all_actors()

BEGIN

SELECT a.id, a.first_name, a.last_name, a.birth_date FROM t_actor a;

END;

To call this procedure you declare the RowMapper. Because the class you want to map to follows the

JavaBean rules, you can use a ParameterizedBeanPropertyRowMapper that is created by passing

in the required class to map to in the newInstance method.

public class JdbcActorDao implements ActorDao {

private SimpleJdbcCall procReadAllActors;

public void setDataSource(DataSource dataSource) {

JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

jdbcTemplate.setResultsMapCaseInsensitive(true);

this.procReadAllActors = new SimpleJdbcCall(jdbcTemplate)

.withProcedureName("read_all_actors")

.returningResultSet("actors",

ParameterizedBeanPropertyRowMapper.newInstance(Actor.class));

}

public List getActorsList() {

Map m = procReadAllActors.execute(new HashMap<String, Object>(0));

return (List) m.get("actors");

}

// ... additional methods

}

The execute call passes in an empty Map because this call does not take any parameters. The list of

Actors is then retrieved from the results map and returned to the caller.

14.6 Modeling JDBC operations as Java objects

The org.springframework.jdbc.object package contains classes that allow you to access the

database in a more object-oriented manner. As an example, you can execute queries and get the results

back as a list containing business objects with the relational column data mapped to the properties of the

business object. You can also execute stored procedures and run update, delete, and insert statements.

Note

Many Spring developers believe that the various RDBMS operation classes described below

(with the exception of the StoredProcedure class) can often be replaced with straight

JdbcTemplate calls. Often it is simpler to write a DAO method that simply calls a method on a

JdbcTemplate directly (as opposed to encapsulating a query as a full-blown class).

However, if you are getting measurable value from using the RDBMS operation classes, continue

using these classes.

SqlQuery

SqlQuery is a reusable, threadsafe class that encapsulates an SQL query. Subclasses must implement

the newRowMapper(..) method to provide a RowMapper instance that can create one object per

row obtained from iterating over the ResultSet that is created during the execution of the query. The

SqlQuery class is rarely used directly because the MappingSqlQuery subclass provides a much

more convenient implementation for mapping rows to Java classes. Other implementations that extend

SqlQuery are MappingSqlQueryWithParameters and UpdatableSqlQuery.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 390

MappingSqlQuery

MappingSqlQuery is a reusable query in which concrete subclasses must implement the abstract

mapRow(..) method to convert each row of the supplied ResultSet into an object of the type

specified. The following example shows a custom query that maps the data from the t_actor relation

to an instance of the Actor class.

public class ActorMappingQuery extends MappingSqlQuery<Actor> {

public ActorMappingQuery(DataSource ds) {

super(ds, "select id, first_name, last_name from t_actor where id = ?");

super.declareParameter(new SqlParameter("id", Types.INTEGER));

compile();

}

@Override

protected Actor mapRow(ResultSet rs, int rowNumber) throws SQLException {

Actor actor = new Actor();

actor.setId(rs.getLong("id"));

actor.setFirstName(rs.getString("first_name"));

actor.setLastName(rs.getString("last_name"));

return actor;

}

The class extends MappingSqlQuery parameterized with the Actor type. The constructor for this

customer query takes the DataSource as the only parameter. In this constructor you call the constructor

on the superclass with the DataSource and the SQL that should be executed to retrieve the rows

for this query. This SQL will be used to create a PreparedStatement so it may contain place

holders for any parameters to be passed in during execution.You must declare each parameter using

the declareParameter method passing in an SqlParameter. The SqlParameter takes a name

and the JDBC type as defined in java.sql.Types. After you define all parameters, you call the

compile() method so the statement can be prepared and later executed. This class is thread-safe

after it is compiled, so as long as these instances are created when the DAO is initialized they can be

kept as instance variables and be reused.

private ActorMappingQuery actorMappingQuery;

@Autowired

public void setDataSource(DataSource dataSource) {

this.actorMappingQuery = new ActorMappingQuery(dataSource);

}

public Customer getCustomer(Long id) {

return actorMappingQuery.findObject(id);

}

The method in this example retrieves the customer with the id that is passed in as the only parameter.

Since we only want one object returned we simply call the convenience method findObject with the

id as parameter. If we had instead a query that returned a list of objects and took additional parameters

then we would use one of the execute methods that takes an array of parameter values passed in as

varargs.

public List<Actor> searchForActors(int age, String namePattern) {

List<Actor> actors = actorSearchMappingQuery.execute(age, namePattern);

return actors;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 391

SqlUpdate

The SqlUpdate class encapsulates an SQL update. Like a query, an update object is reusable, and

like all RdbmsOperation classes, an update can have parameters and is defined in SQL. This class

provides a number of update(..) methods analogous to the execute(..) methods of query objects.

The SQLUpdate class is concrete. It can be subclassed, for example, to add a custom update method,

as in the following snippet where it’s simply called execute. However, you don’t have to subclass the

SqlUpdate class since it can easily be parameterized by setting SQL and declaring parameters.

import java.sql.Types;

import javax.sql.DataSource;

import org.springframework.jdbc.core.SqlParameter;

import org.springframework.jdbc.object.SqlUpdate;

public class UpdateCreditRating extends SqlUpdate {

public UpdateCreditRating(DataSource ds) {

setDataSource(ds);

setSql("update customer set credit_rating = ? where id = ?");

declareParameter(new SqlParameter("creditRating", Types.NUMERIC));

declareParameter(new SqlParameter("id", Types.NUMERIC));

compile();

}

/**

* @param id for the Customer to be updated

* @param rating the new value for credit rating

* @return number of rows updated

public int execute(int id, int rating) {

return update(rating, id);

}

StoredProcedure

The StoredProcedure class is a superclass for object abstractions of RDBMS stored procedures.

This class is abstract, and its various execute(..) methods have protected access, preventing

use other than through a subclass that offers tighter typing.

The inherited sql property will be the name of the stored procedure in the RDBMS.

To define a parameter for the StoredProcedure class, you use an SqlParameter or one of its

subclasses. You must specify the parameter name and SQL type in the constructor like in the following

code snippet. The SQL type is specified using the java.sql.Types constants.

new SqlParameter("in_id", Types.NUMERIC),

new SqlOutParameter("out_first_name", Types.VARCHAR),

The first line with the SqlParameter declares an IN parameter. IN parameters can be used for both

stored procedure calls and for queries using the SqlQuery and its subclasses covered in the following

section.

The second line with the SqlOutParameter declares an out parameter to be used in the stored

procedure call. There is also an SqlInOutParameter for I nOut parameters, parameters that provide

an in value to the procedure and that also return a value.

For i n parameters, in addition to the name and the SQL type, you can specify a scale for numeric

data or a type name for custom database types. For out parameters you can provide a RowMapper to

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 392

handle mapping of rows returned from a REF cursor. Another option is to specify an SqlReturnType

that enables you to define customized handling of the return values.

Here is an example of a simple DAO that uses a StoredProcedure to call a function,

sysdate(),which comes with any Oracle database. To use the stored procedure functionality you have

to create a class that extends StoredProcedure. In this example, the StoredProcedure class is

an inner class, but if you need to reuse the StoredProcedure you declare it as a top-level class. This

example has no input parameters, but an output parameter is declared as a date type using the class

SqlOutParameter. The execute() method executes the procedure and extracts the returned date

from the results Map. The results Map has an entry for each declared output parameter, in this case only

one, using the parameter name as the key.

import java.sql.Types;

import java.util.Date;

import java.util.HashMap;

import java.util.Map;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.jdbc.core.SqlOutParameter;

import org.springframework.jdbc.object.StoredProcedure;

public class StoredProcedureDao {

private GetSysdateProcedure getSysdate;

@Autowired

public void init(DataSource dataSource) {

this.getSysdate = new GetSysdateProcedure(dataSource);

}

public Date getSysdate() {

return getSysdate.execute();

}

private class GetSysdateProcedure extends StoredProcedure {

private static final String SQL = "sysdate";

public GetSysdateProcedure(DataSource dataSource) {

setDataSource(dataSource);

setFunction(true);

setSql(SQL);

declareParameter(new SqlOutParameter("date", Types.DATE));

compile();

}

public Date execute() {

// the sysdate sproc has no input parameters, so an empty Map is supplied...

Map<String, Object> results = execute(new HashMap<String, Object>());

Date sysdate = (Date) results.get("date");

return sysdate;

}

The following example of a StoredProcedure has two output parameters (in this case, Oracle REF

cursors).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 393

import oracle.jdbc.OracleTypes;

import org.springframework.jdbc.core.SqlOutParameter;

import org.springframework.jdbc.object.StoredProcedure;

import javax.sql.DataSource;

import java.util.HashMap;

import java.util.Map;

public class TitlesAndGenresStoredProcedure extends StoredProcedure {

private static final String SPROC_NAME = "AllTitlesAndGenres";

public TitlesAndGenresStoredProcedure(DataSource dataSource) {

super(dataSource, SPROC_NAME);

declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));

declareParameter(new SqlOutParameter("genres", OracleTypes.CURSOR, new GenreMapper()));

compile();

}

public Map<String, Object> execute() {

// again, this sproc has no input parameters, so an empty Map is supplied

return super.execute(new HashMap<String, Object>());

}

Notice how the overloaded variants of the declareParameter(..) method that have been used

in the TitlesAndGenresStoredProcedure constructor are passed RowMapper implementation

instances; this is a very convenient and powerful way to reuse existing functionality. The code for the

two RowMapper implementations is provided below.

The TitleMapper class maps a ResultSet to a Title domain object for each row in the supplied

ResultSet:

import org.springframework.jdbc.core.RowMapper;

import java.sql.ResultSet;

import java.sql.SQLException;

import com.foo.domain.Title;

public final class TitleMapper implements RowMapper<Title> {

public Title mapRow(ResultSet rs, int rowNum) throws SQLException {

Title title = new Title();

title.setId(rs.getLong("id"));

title.setName(rs.getString("name"));

return title;

}

The GenreMapper class maps a ResultSet to a Genre domain object for each row in the supplied

ResultSet.

import org.springframework.jdbc.core.RowMapper;

import java.sql.ResultSet;

import java.sql.SQLException;

import com.foo.domain.Genre;

public final class GenreMapper implements RowMapper<Genre> {

public Genre mapRow(ResultSet rs, int rowNum) throws SQLException {

return new Genre(rs.getString("name"));

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 394

To pass parameters to a stored procedure that has one or more input parameters in its definition in the

RDBMS, you can code a strongly typed execute(..) method that would delegate to the superclass'

untyped execute(Map parameters) method (which has protected access); for example:

import oracle.jdbc.OracleTypes;

import org.springframework.jdbc.core.SqlOutParameter;

import org.springframework.jdbc.core.SqlParameter;

import org.springframework.jdbc.object.StoredProcedure;

import javax.sql.DataSource;

import java.sql.Types;

import java.util.Date;

import java.util.HashMap;

import java.util.Map;

public class TitlesAfterDateStoredProcedure extends StoredProcedure {

private static final String SPROC_NAME = "TitlesAfterDate";

private static final String CUTOFF_DATE_PARAM = "cutoffDate";

public TitlesAfterDateStoredProcedure(DataSource dataSource) {

super(dataSource, SPROC_NAME);

declareParameter(new SqlParameter(CUTOFF_DATE_PARAM, Types.DATE);

declareParameter(new SqlOutParameter("titles", OracleTypes.CURSOR, new TitleMapper()));

compile();

}

public Map<String, Object> execute(Date cutoffDate) {

Map<String, Object> inputs = new HashMap<String, Object>();

inputs.put(CUTOFF_DATE_PARAM, cutoffDate);

return super.execute(inputs);

}

14.7 Common problems with parameter and data value

handling

Common problems with parameters and data values exist in the different approaches provided by the

Spring Framework JDBC.

Providing SQL type information for parameters

Usually Spring determines the SQL type of the parameters based on the type of parameter passed

in. It is possible to explicitly provide the SQL type to be used when setting parameter values. This is

sometimes necessary to correctly set NULL values.

You can provide SQL type information in several ways:

• Many update and query methods of the JdbcTemplate take an additional parameter in the form

of an int array. This array is used to indicate the SQL type of the corresponding parameter using

constant values from the java.sql.Types class. Provide one entry for each parameter.

• You can use the SqlParameterValue class to wrap the parameter value that needs this additional

information.Create a new instance for each value and pass in the SQL type and parameter value in

the constructor. You can also provide an optional scale parameter for numeric values.

• For methods working with named parameters, use the SqlParameterSource classes

BeanPropertySqlParameterSource or MapSqlParameterSource. They both have methods

for registering the SQL type for any of the named parameter values.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 395

Handling BLOB and CLOB objects

You can store images, other binary objects, and large chunks of text. These large object are called BLOB

for binary data and CLOB for character data. In Spring you can handle these large objects by using the

JdbcTemplate directly and also when using the higher abstractions provided by RDBMS Objects and the

SimpleJdbc classes. All of these approaches use an implementation of the LobHandler interface for

the actual management of the LOB data. The LobHandler provides access to a LobCreator class,

through the getLobCreator method, used for creating new LOB objects to be inserted.

The LobCreator/LobHandler provides the following support for LOB input and output:

• BLOB

• byte[] — getBlobAsBytes and setBlobAsBytes

• InputStream — getBlobAsBinaryStream and setBlobAsBinaryStream

• CLOB

• String — getClobAsString and setClobAsString

• InputStream — getClobAsAsciiStream and setClobAsAsciiStream

• Reader — getClobAsCharacterStream and setClobAsCharacterStream

The next example shows how to create and insert a BLOB. Later you will see how to read it back from

the database.

This example uses a JdbcTemplate and an implementation of the

AbstractLobCreatingPreparedStatementCallbac k. It implements one method, setValues.

This method provides a LobCreator that you use to set the values for the LOB columns in your SQL

insert statement.

For this example we assume that there is a variable, lobHandle r, that already is set to an instance

of a DefaultLobHandler. You typically set this value through dependency injection.

final File blobIn = new File("spring2004.jpg");

final InputStream blobIs = new FileInputStream(blobIn);

final File clobIn = new File("large.txt");

final InputStream clobIs = new FileInputStream(clobIn);

final InputStreamReader clobReader = new InputStreamReader(clobIs);

jdbcTemplate.execute(

"INSERT INTO lob_table (id, a_clob, a_blob) VALUES (?, ?, ?)",

new AbstractLobCreatingPreparedStatementCallback(lobHandler) { ❶

protected void setValues(PreparedStatement ps, LobCreator lobCreator) throws SQLException {

ps.setLong(1, 1L);

lobCreator.setClobAsCharacterStream(ps, 2, clobReader, (int)clobIn.length()); ❷

lobCreator.setBlobAsBinaryStream(ps, 3, blobIs, (int)blobIn.length()); ❸

}

);

blobIs.close();

clobReader.close();

❶Pass in the lobHandler that in this example is a plain DefaultLobHandler

❷Using the method setClobAsCharacterStream, pass in the contents of the CLOB.

❸Using the method setBlobAsBinaryStream, pass in the contents of the BLOB.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 396

Now it’s time to read the LOB data from the database. Again, you use a JdbcTemplate with the same

instance variable l obHandler and a reference to a DefaultLobHandler.

List<Map<String, Object>> l = jdbcTemplate.query("select id, a_clob, a_blob from lob_table",

new RowMapper<Map<String, Object>>() {

public Map<String, Object> mapRow(ResultSet rs, int i) throws SQLException {

Map<String, Object> results = new HashMap<String, Object>();

String clobText = lobHandler.getClobAsString(rs, "a_clob"); ❶

results.put("CLOB", clobText); byte[] blobBytes = lobHandler.getBlobAsBytes(rs, "a_blob"); ❷

results.put("BLOB", blobBytes); return results; } });

❶Using the method getClobAsString, retrieve the contents of the CLOB.

❷Using the method getBlobAsBytes, retrieve the contents of the BLOB.

Passing in lists of values for IN clause

The SQL standard allows for selecting rows based on an expression that includes a variable list

of values. A typical example would be select * from T_ACTOR where id in (1,

2, 3). This variable list is not directly supported for prepared statements by the JDBC standard;

you cannot declare a variable number of placeholders. You need a number of variations with the

desired number of placeholders prepared, or you need to generate the SQL string dynamically

once you know how many placeholders are required. The named parameter support provided in the

NamedParameterJdbcTemplate and JdbcTemplate takes the latter approach. Pass in the values

as a java.util.List of primitive objects. This list will be used to insert the required placeholders and

pass in the values during the statement execution.

Note

Be careful when passing in many values. The JDBC standard does not guarantee that you can

use more than 100 values for an in expression list. Various databases exceed this number, but

they usually have a hard limit for how many values are allowed. Oracle’s limit is 1000.

In addition to the primitive values in the value list, you can create a java.util.List of object arrays.

This list would support multiple expressions defined for the in clause such as select * from

T_ACTOR where (id, last_name) in ((1, 'Johnson'), (2, 'Harrop')). This of course

requires that your database supports this syntax.

Handling complex types for stored procedure calls

When you call stored procedures you can sometimes use complex types specific to the database.

To accommodate these types, Spring provides a SqlReturnType for handling them when they are

returned from the stored procedure call and SqlTypeValue when they are passed in as a parameter

to the stored procedure.

Here is an example of returning the value of an Oracle STRUCT object of the user declared type

ITEM_TYPE. The SqlReturnType interface has a single method named getTypeValue that must be

implemented. This interface is used as part of the declaration of an SqlOutParameter.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 397

final TestItem = new TestItem(123L, "A test item",

new SimpleDateFormat("yyyy-M-d").parse("2010-12-31"));

declareParameter(new SqlOutParameter("item", OracleTypes.STRUCT, "ITEM_TYPE",

new SqlReturnType() {

public Object getTypeValue(CallableStatement cs, int colIndx, int sqlType, String

typeName) throws SQLException {

STRUCT struct = (STRUCT) cs.getObject(colIndx);

Object[] attr = struct.getAttributes();

TestItem item = new TestItem();

item.setId(((Number) attr[0]).longValue());

item.setDescription((String) attr[1]);

item.setExpirationDate((java.util.Date) attr[2]);

return item;

}

}));

You use the SqlTypeValue to pass in the value of a Java object like TestItem into a stored

procedure. The SqlTypeValue interface has a single method named createTypeValue that you

must implement. The active connection is passed in, and you can use it to create database-specific

objects such as StructDescriptors, as shown in the following example, or ArrayDescriptors.

final TestItem = new TestItem(123L, "A test item",

new SimpleDateFormat("yyyy-M-d").parse("2010-12-31"));

SqlTypeValue value = new AbstractSqlTypeValue() {

protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException

{

StructDescriptor itemDescriptor = new StructDescriptor(typeName, conn);

Struct item = new STRUCT(itemDescriptor, conn,

new Object[] {

testItem.getId(),

testItem.getDescription(),

new java.sql.Date(testItem.getExpirationDate().getTime())

});

return item;

}

};

This SqlTypeValue can now be added to the Map containing the input parameters for the execute

call of the stored procedure.

Another use for the SqlTypeValue is passing in an array of values to an Oracle stored procedure.

Oracle has its own internal ARRAY class that must be used in this case, and you can use the

SqlTypeValue to create an instance of the Oracle ARRAY and populate it with values from the Java

ARRAY.

final Long[] ids = new Long[] {1L, 2L};

SqlTypeValue value = new AbstractSqlTypeValue() {

protected Object createTypeValue(Connection conn, int sqlType, String typeName) throws SQLException

{

ArrayDescriptor arrayDescriptor = new ArrayDescriptor(typeName, conn);

ARRAY idArray = new ARRAY(arrayDescriptor, conn, ids);

return idArray;

}

};

14.8 Embedded database support

The org.springframework.jdbc.datasource.embedded package provides support for

embedded Java database engines. Support for HSQL, H2, and Derby is provided natively. You can also

use an extensible API to plug in new embedded database types and DataSource implementations.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 398

Why use an embedded database?

An embedded database is useful during the development phase of a project because of its lightweight

nature. Benefits include ease of configuration, quick startup time, testability, and the ability to rapidly

evolve SQL during development.

Creating an embedded database instance using Spring XML

If you want to expose an embedded database instance as a bean in a Spring ApplicationContext, use

the embedded-database tag in the spring-jdbc namespace:

<jdbc:embedded-database id="dataSource">

<jdbc:script location="classpath:schema.sql"/>

<jdbc:script location="classpath:test-data.sql"/>

</jdbc:embedded-database>

The preceding configuration creates an embedded HSQL database populated with SQL from

schema.sql and testdata.sql resources in the classpath. The database instance is made available to

the Spring container as a bean of type javax.sql.DataSource. This bean can then be injected into

data access objects as needed.

Creating an embedded database instance programmatically

The EmbeddedDatabaseBuilder class provides a fluent API for constructing an embedded database

programmatically. Use this when you need to create an embedded database instance in a standalone

environment, such as a data access object unit test:

EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();

EmbeddedDatabase db = builder.setType(H2).addScript("my-schema.sql").addScript("my-test-

data.sql").build();

// do stuff against the db (EmbeddedDatabase extends javax.sql.DataSource)

db.shutdown()

Extending the embedded database support

Spring JDBC embedded database support can be extended in two ways:

• Implement EmbeddedDatabaseConfigurer to support a new embedded database type, such as

Apache Derby.

• Implement DataSourceFactory to support a new DataSource implementation, such as a

connection pool, to manage embedded database connections.

You are encouraged to contribute back extensions to the Spring community at jira.spring.io.

Using HSQL

Spring supports HSQL 1.8.0 and above. HSQL is the default embedded database if no type is specified

explicitly. To specify HSQL explicitly, set the type attribute of the embedded-database tag to

HSQL. If you are using the builder API, call the setType(EmbeddedDatabaseType) method with

EmbeddedDatabaseType.HSQL.

Using H2

Spring supports the H2 database as well. To enable H2, set the type attribute of the embedded-

database tag to H2. If you are using the builder API, call the setType(EmbeddedDatabaseType)

method with EmbeddedDatabaseType.H2.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 399

Using Derby

Spring also supports Apache Derby 10.5 and above. To enable Derby, set the type

attribute of the embedded-database tag to Derby. If using the builder API, call the

setType(EmbeddedDatabaseType) method with EmbeddedDatabaseType.Derby.

Testing data access logic with an embedded database

Embedded databases provide a lightweight way to test data access code. The following is a data access

unit test template that uses an embedded database:

public class DataAccessUnitTestTemplate {

private EmbeddedDatabase db;

@Before

public void setUp() {

// creates an HSQL in-memory database populated from default scripts

// classpath:schema.sql and classpath:data.sql

db = new EmbeddedDatabaseBuilder().addDefaultScripts().build();

}

@Test

public void testDataAccess() {

JdbcTemplate template = new JdbcTemplate(db);

template.query(...);

}

@After

public void tearDown() {

db.shutdown();

}

14.9 Initializing a DataSource

The org.springframework.jdbc.datasource.init package provides support for initializing an

existing DataSource. The embedded database support provides one option for creating and initializing

a DataSource for an application, but sometimes you need to initialize an instance running on a server

somewhere.

Initializing a database instance using Spring XML

If you want to initialize a database and you can provide a reference to a DataSource bean, use the

initialize-database tag in the spring-jdbc namespace:

<jdbc:initialize-database data-source="dataSource">

<jdbc:script location="classpath:com/foo/sql/db-schema.sql"/>

<jdbc:script location="classpath:com/foo/sql/db-test-data.sql"/>

</jdbc:initialize-database>

The example above runs the two scripts specified against the database: the first script is a schema

creation, and the second is a test data set insert. The script locations can also be patterns with

wildcards in the usual ant style used for resources in Spring (e.g. classpath*:/com/foo/**/sql/

*-data.sql). If a pattern is used the scripts are executed in lexical order of their URL or filename.

The default behavior of the database initializer is to unconditionally execute the scripts provided. This

will not always be what you want, for instance if running against an existing database that already has

test data in it. The likelihood of accidentally deleting data is reduced by the commonest pattern (as

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 400

shown above) that creates the tables first and then inserts the data - the first step will fail if the tables

already exist.

However, to get more control over the creation and deletion of existing data, the XML namespace

provides a couple more options. The first is flag to switch the initialization on and off. This can be set

according to the environment (e.g. to pull a boolean value from system properties or an environment

bean), e.g.

<jdbc:initialize-database data-source="dataSource"

enabled="#{systemProperties.INITIALIZE_DATABASE}">

<jdbc:script location="..."/>

</jdbc:initialize-database>

The second option to control what happens with existing data is to be more tolerant of failures. To this

end you can control the ability of the initializer to ignore certain errors in the SQL it executes from the

scripts, e.g.

<jdbc:initialize-database data-source="dataSource" ignore-failures="DROPS">

<jdbc:script location="..."/>

</jdbc:initialize-database>

In this example we are saying we expect that sometimes the scripts will be run against an empty

database and there are some DROP statements in the scripts which would therefore fail. So failed SQL

DROP statements will be ignored, but other failures will cause an exception. This is useful if your SQL

dialect doesn’t support DROP ... IF EXISTS (or similar) but you want to unconditionally remove all

test data before re-creating it. In that case the first script is usually a set of drops, followed by a set of

CREATE statements.

The ignore-failures option can be set to NONE (the default), DROPS (ignore failed drops) or ALL

(ignore all failures).

If you need more control than you get from the XML namespace, you can simply use the

DataSourceInitializer directly, and define it as a component in your application.

Initialization of Other Components that Depend on the Database

A large class of applications can just use the database initializer with no further complications: those

that do not use the database until after the Spring context has started. If your application is not one of

those then you might need to read the rest of this section.

The database initializer depends on a data source instance and runs the scripts provided in its

initialization callback (c.f. init-method in an XML bean definition or InitializingBean). If other

beans depend on the same data source and also use the data source in an initialization callback then

there might be a problem because the data has not yet been initialized. A common example of this is a

cache that initializes eagerly and loads up data from the database on application startup.

To get round this issue you two options: change your cache initialization strategy to a later phase, or

ensure that the database initializer is initialized first.

The first option might be easy if the application is in your control, and not otherwise. Some suggestions

for how to implement this are

• Make the cache initialize lazily on first usage, which improves application startup time

• Have your cache or a separate component that initializes the cache implement Lifecycle or

SmartLifecycle. When the application context starts up a SmartLifecycle can be automatically

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 401

started if its autoStartup flag is set, and a Lifecycle can be started manually by calling

ConfigurableApplicationContext.start() on the enclosing context.

• Use a Spring ApplicationEvent or similar custom observer mechanism to trigger the cache

initialization. ContextRefreshedEvent is always published by the context when it is ready for use

(after all beans have been initialized), so that is often a useful hook (this is how the SmartLifecycle

works by default).

The second option can also be easy. Some suggestions on how to implement this are

• Rely on Spring BeanFactory default behavior, which is that beans are initialized in registration order.

You can easily arrange that by adopting the common practice of a set of <import/> elements that order

your application modules, and ensure that the database and database initialization are listed first

• Separate the datasource and the business components that use it and control their startup order by

putting them in separate ApplicationContext instances (e.g. parent has the datasource and child has

the business components). This structure is common in Spring web applications, but can be more

generally applied.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 402

15. Object Relational Mapping (ORM) Data Access

15.1 Introduction to ORM with Spring

The Spring Framework supports integration with Hibernate, Java Persistence API (JPA) and Java Data

Objects (JDO) for resource management, data access object (DAO) implementations, and transaction

strategies. For example, for Hibernate there is first-class support with several convenient IoC features

that address many typical Hibernate integration issues. You can configure all of the supported features

for O/R (object relational) mapping tools through Dependency Injection. They can participate in Spring’s

resource and transaction management, and they comply with Spring’s generic transaction and DAO

exception hierarchies. The recommended integration style is to code DAOs against plain Hibernate,

JPA, and JDO APIs. The older style of using Spring’s DAO templates is no longer recommended;

however, coverage of this style can be found in the Section 32.1, “Classic ORM usage” in the

appendices.

Spring adds significant enhancements to the ORM layer of your choice when you create data access

applications. You can leverage as much of the integration support as you wish, and you should compare

this integration effort with the cost and risk of building a similar infrastructure in-house. You can use much

of the ORM support as you would a library, regardless of technology, because everything is designed as

a set of reusable JavaBeans. ORM in a Spring IoC container facilitates configuration and deployment.

Thus most examples in this section show configuration inside a Spring container.

Benefits of using the Spring Framework to create your ORM DAOs include:

•Easier testing. Spring’s IoC approach makes it easy to swap the implementations and configuration

locations of Hibernate SessionFactory instances, JDBC DataSource instances, transaction

managers, and mapped object implementations (if needed). This in turn makes it much easier to test

each piece of persistence-related code in isolation.

•Common data access exceptions. Spring can wrap exceptions from your ORM tool, converting

them from proprietary (potentially checked) exceptions to a common runtime DataAccessException

hierarchy. This feature allows you to handle most persistence exceptions, which are non-recoverable,

only in the appropriate layers, without annoying boilerplate catches, throws, and exception

declarations. You can still trap and handle exceptions as necessary. Remember that JDBC exceptions

(including DB-specific dialects) are also converted to the same hierarchy, meaning that you can

perform some operations with JDBC within a consistent programming model.

•General resource management. Spring application contexts can handle the location and configuration

of Hibernate SessionFactory instances, JPA EntityManagerFactory instances, JDBC

DataSource instances, and other related resources. This makes these values easy to manage and

change. Spring offers efficient, easy, and safe handling of persistence resources. For example, related

code that uses Hibernate generally needs to use the same Hibernate Session to ensure efficiency

and proper transaction handling. Spring makes it easy to create and bind a Session to the current

thread transparently, by exposing a current Session through the Hibernate SessionFactory. Thus

Spring solves many chronic problems of typical Hibernate usage, for any local or JTA transaction

environment.

•Integrated transaction management. You can wrap your ORM code with a declarative, aspect-oriented

programming (AOP) style method interceptor either through the @Transactional annotation or

by explicitly configuring the transaction AOP advice in an XML configuration file. In both cases,

transaction semantics and exception handling (rollback, and so on) are handled for you. As discussed

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 403

below, in Resource and transaction management, you can also swap various transaction managers,

without affecting your ORM-related code. For example, you can swap between local transactions

and JTA, with the same full services (such as declarative transactions) available in both scenarios.

Additionally, JDBC-related code can fully integrate transactionally with the code you use to do ORM.

This is useful for data access that is not suitable for ORM, such as batch processing and BLOB

streaming, which still need to share common transactions with ORM operations.

Tip

For more comprehensive ORM support, including support for alternative database technologies

such as MongoDB, you might want to check out the Spring Data suite of projects. If you are a

JPA user, the Getting Started Accessing Data with JPA guide from https://spring.io provides a

great introduction.

15.2 General ORM integration considerations

This section highlights considerations that apply to all ORM technologies. The Section 15.3, “Hibernate”

section provides more details and also show these features and configurations in a concrete context.

The major goal of Spring’s ORM integration is clear application layering, with any data access and

transaction technology, and for loose coupling of application objects. No more business service

dependencies on the data access or transaction strategy, no more hard-coded resource lookups,

no more hard-to-replace singletons, no more custom service registries. One simple and consistent

approach to wiring up application objects, keeping them as reusable and free from container

dependencies as possible. All the individual data access features are usable on their own but

integrate nicely with Spring’s application context concept, providing XML-based configuration and cross-

referencing of plain JavaBean instances that need not be Spring-aware. In a typical Spring application,

many important objects are JavaBeans: data access templates, data access objects, transaction

managers, business services that use the data access objects and transaction managers, web view

resolvers, web controllers that use the business services,and so on.

Resource and transaction management

Typical business applications are cluttered with repetitive resource management code. Many projects

try to invent their own solutions, sometimes sacrificing proper handling of failures for programming

convenience. Spring advocates simple solutions for proper resource handling, namely IoC through

templating in the case of JDBC and applying AOP interceptors for the ORM technologies.

The infrastructure provides proper resource handling and appropriate conversion of specific API

exceptions to an unchecked infrastructure exception hierarchy. Spring introduces a DAO exception

hierarchy, applicable to any data access strategy. For direct JDBC, the JdbcTemplate class mentioned

in a previous section provides connection handling and proper conversion of SQLException to the

DataAccessException hierarchy, including translation of database-specific SQL error codes to

meaningful exception classes. For ORM technologies, see the next section for how to get the same

exception translation benefits.

When it comes to transaction management, the JdbcTemplate class hooks in to the Spring transaction

support and supports both JTA and JDBC transactions, through respective Spring transaction

managers. For the supported ORM technologies Spring offers Hibernate, JPA and JDO support through

the Hibernate, JPA, and JDO transaction managers as well as JTA support. For details on transaction

support, see the Chapter 12, Transaction Management chapter.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 404

Exception translation

When you use Hibernate, JPA, or JDO in a DAO, you must decide how to handle the persistence

technology’s native exception classes. The DAO throws a subclass of a HibernateException,

PersistenceException or JDOException depending on the technology. These exceptions are

all run-time exceptions and do not have to be declared or caught. You may also have to deal with

IllegalArgumentException and IllegalStateException. This means that callers can only

treat exceptions as generally fatal, unless they want to depend on the persistence technology’s own

exception structure. Catching specific causes such as an optimistic locking failure is not possible without

tying the caller to the implementation strategy. This trade off might be acceptable to applications that

are strongly ORM-based and/or do not need any special exception treatment. However, Spring enables

exception translation to be applied transparently through the @Repository annotation:

@Repository

public class ProductDaoImpl implements ProductDao {

// class body here...

}

<beans>

</beans>

The postprocessor automatically looks for all exception translators (implementations of the

PersistenceExceptionTranslator interface) and advises all beans marked with the

@Repository annotation so that the discovered translators can intercept and apply the appropriate

translation on the thrown exceptions.

In summary: you can implement DAOs based on the plain persistence technology’s API and annotations,

while still benefiting from Spring-managed transactions, dependency injection, and transparent

exception conversion (if desired) to Spring’s custom exception hierarchies.

15.3 Hibernate

We will start with a coverage of Hibernate 3 in a Spring environment, using it to demonstrate the

approach that Spring takes towards integrating O/R mappers. This section will cover many issues in

detail and show different variations of DAO implementations and transaction demarcation. Most of these

patterns can be directly translated to all other supported ORM tools. The following sections in this chapter

will then cover the other ORM technologies, showing briefer examples there.

Note

As of Spring 4.0, Spring requires Hibernate 3.6 or later.

SessionFactory setup in a Spring container

To avoid tying application objects to hard-coded resource lookups, you can define resources such as

a JDBC DataSource or a Hibernate SessionFactory as beans in the Spring container. Application

objects that need to access resources receive references to such predefined instances through bean

references, as illustrated in the DAO definition in the next section.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 405

The following excerpt from an XML application context definition shows how to set up a JDBC

DataSource and a Hibernate SessionFactory on top of it:

<beans>

</bean>

<list>

<value>product.hbm.xml</value>

</list>

</property>

<value>

hibernate.dialect=org.hibernate.dialect.HSQLDialect

</value>

</property>

</bean>

</beans>

Switching from a local Jakarta Commons DBCP BasicDataSource to a JNDI-located DataSource

(usually managed by an application server) is just a matter of configuration:

<beans>

<jee:jndi-lookup id="myDataSource" jndi-name="java:comp/env/jdbc/myds"/>

</beans>

You can also access a JNDI-located SessionFactory, using Spring’s JndiObjectFactoryBean /

<jee:jndi-lookup> to retrieve and expose it. However, that is typically not common outside of an

EJB context.

Implementing DAOs based on plain Hibernate 3 API

Hibernate 3 has a feature called contextual sessions, wherein Hibernate itself manages one current

Session per transaction. This is roughly equivalent to Spring’s synchronization of one Hibernate

Session per transaction. A corresponding DAO implementation resembles the following example,

based on the plain Hibernate API:

public class ProductDaoImpl implements ProductDao {

private SessionFactory sessionFactory;

public void setSessionFactory(SessionFactory sessionFactory) {

this.sessionFactory = sessionFactory;

}

public Collection loadProductsByCategory(String category) {

return this.sessionFactory.getCurrentSession()

.createQuery("from test.Product product where product.category=?")

.setParameter(0, category)

.list();

}

This style is similar to that of the Hibernate reference documentation and examples, except for holding

the SessionFactory in an instance variable. We strongly recommend such an instance-based

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 406

setup over the old-school static HibernateUtil class from Hibernate’s CaveatEmptor sample

application. (In general, do not keep any resources in static variables unless absolutely necessary.)

The above DAO follows the dependency injection pattern: it fits nicely into a Spring IoC container, just

as it would if coded against Spring’s HibernateTemplate. Of course, such a DAO can also be set up

in plain Java (for example, in unit tests). Simply instantiate it and call setSessionFactory(..) with

the desired factory reference. As a Spring bean definition, the DAO would resemble the following:

<beans>

</bean>

</beans>

The main advantage of this DAO style is that it depends on Hibernate API only; no import of any Spring

class is required. This is of course appealing from a non-invasiveness perspective, and will no doubt

feel more natural to Hibernate developers.

However, the DAO throws plain HibernateException (which is unchecked, so does not have to

be declared or caught), which means that callers can only treat exceptions as generally fatal - unless

they want to depend on Hibernate’s own exception hierarchy. Catching specific causes such as an

optimistic locking failure is not possible without tying the caller to the implementation strategy. This trade

off might be acceptable to applications that are strongly Hibernate-based and/or do not need any special

exception treatment.

Fortunately, Spring’s LocalSessionFactoryBean supports Hibernate’s

SessionFactory.getCurrentSession() method for any Spring transaction strategy, returning

the current Spring-managed transactional Session even with HibernateTransactionManager. Of

course, the standard behavior of that method remains the return of the current Session associated with

the ongoing JTA transaction, if any. This behavior applies regardless of whether you are using Spring’s

JtaTransactionManager, EJB container managed transactions (CMTs), or JTA.

In summary: you can implement DAOs based on the plain Hibernate 3 API, while still being able to

participate in Spring-managed transactions.

Declarative transaction demarcation

We recommend that you use Spring’s declarative transaction support, which enables you to replace

explicit transaction demarcation API calls in your Java code with an AOP transaction interceptor.

This transaction interceptor can be configured in a Spring container using either Java annotations

or XML.This declarative transaction capability allows you to keep business services free of repetitive

transaction demarcation code and to focus on adding business logic, which is the real value of your

application.

Note

Prior to continuing, you are strongly encouraged to read Section 12.5, “Declarative transaction

management” if you have not done so.

Furthermore, transaction semantics like propagation behavior and isolation level can be changed in a

configuration file and do not affect the business service implementations.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 407

The following example shows how you can configure an AOP transaction interceptor, using XML, for

a simple service class:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<bean id="transactionManager"

class="org.springframework.orm.hibernate3.HibernateTransactionManager">

</bean>

<aop:config>

<aop:pointcut id="productServiceMethods"

expression="execution(* product.ProductService.(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/>

</aop:config>

<tx:advice id="txAdvice" transaction-manager="myTxManager">

<tx:attributes>

<tx:method name="increasePrice" propagation="REQUIRED"/>

<tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/>

<tx:method name="*" propagation="SUPPORTS" read-only="true"/>

</tx:attributes>

</tx:advice>

</bean>

</beans>

This is the service class that is advised:

public class ProductServiceImpl implements ProductService {

private ProductDao productDao;

public void setProductDao(ProductDao productDao) {

this.productDao = productDao;

}

// notice the absence of transaction demarcation code in this method

// Spring's declarative transaction infrastructure will be demarcating

// transactions on your behalf

public void increasePriceOfAllProductsInCategory(final String category) {

List productsToChange = this.productDao.loadProductsByCategory(category);

// ...

}

We also show an attribute-support based configuration, in the following example. You annotate the

service layer with @Transactional annotations and instruct the Spring container to find these annotations

and provide transactional semantics for these annotated methods.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 408

public class ProductServiceImpl implements ProductService {

private ProductDao productDao;

public void setProductDao(ProductDao productDao) {

this.productDao = productDao;

}

@Transactional

public void increasePriceOfAllProductsInCategory(final String category) {

List productsToChange = this.productDao.loadProductsByCategory(category);

// ...

}

@Transactional(readOnly = true)

public List<Product> findAllProducts() {

return this.productDao.findAllProducts();

}

As you can see from the following configuration example, the configuration is much simplified, compared

to the XML example above, while still providing the same functionality driven by the annotations in

the service layer code. All you need to provide is the TransactionManager implementation and a

"<tx:annotation-driven/>" entry.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

<bean id="transactionManager"

class="org.springframework.orm.hibernate3.HibernateTransactionManager">

</bean>

<tx:annotation-driven/>

</bean>

</beans>

Programmatic transaction demarcation

You can demarcate transactions in a higher level of the application, on top of such lower-level data

access services spanning any number of operations. Nor do restrictions exist on the implementation

of the surrounding business service; it just needs a Spring PlatformTransactionManager.

Again, the latter can come from anywhere, but preferably as a bean reference through

a setTransactionManager(..) method, just as the productDAO should be set by a

setProductDao(..) method. The following snippets show a transaction manager and a business

service definition in a Spring application context, and an example for a business method implementation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 409

<beans>

</bean>

</bean>

</beans>

public class ProductServiceImpl implements ProductService {

private TransactionTemplate transactionTemplate;

private ProductDao productDao;

public void setTransactionManager(PlatformTransactionManager transactionManager) {

this.transactionTemplate = new TransactionTemplate(transactionManager);

}

public void setProductDao(ProductDao productDao) {

this.productDao = productDao;

}

public void increasePriceOfAllProductsInCategory(final String category) {

this.transactionTemplate.execute(new TransactionCallbackWithoutResult() {

public void doInTransactionWithoutResult(TransactionStatus status) {

List productsToChange = this.productDao.loadProductsByCategory(category);

// do the price increase...

}

});

}

Spring’s TransactionInterceptor allows any checked application exception to be thrown with

the callback code, while TransactionTemplate is restricted to unchecked exceptions within

the callback. TransactionTemplate triggers a rollback in case of an unchecked application

exception, or if the transaction is marked rollback-only by the application (via TransactionStatus).

TransactionInterceptor behaves the same way by default but allows configurable rollback policies

per method.

Transaction management strategies

Both TransactionTemplate and TransactionInterceptor delegate the actual

transaction handling to a PlatformTransactionManager instance, which can be a

HibernateTransactionManager (for a single Hibernate SessionFactory, using a ThreadLocal

Session under the hood) or a JtaTransactionManager (delegating to the JTA subsystem of the

container) for Hibernate applications. You can even use a custom PlatformTransactionManager

implementation. Switching from native Hibernate transaction management to JTA, such as when

facing distributed transaction requirements for certain deployments of your application, is just a matter

of configuration. Simply replace the Hibernate transaction manager with Spring’s JTA transaction

implementation. Both transaction demarcation and data access code will work without changes,

because they just use the generic transaction management APIs.

For distributed transactions across multiple Hibernate session factories, simply combine

JtaTransactionManager as a transaction strategy with multiple LocalSessionFactoryBean

definitions. Each DAO then gets one specific SessionFactory reference passed into its corresponding

bean property. If all underlying JDBC data sources are transactional container ones, a business service

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 410

can demarcate transactions across any number of DAOs and any number of session factories without

special regard, as long as it is using JtaTransactionManager as the strategy.

<beans>

<jee:jndi-lookup id="dataSource1" jndi-name="java:comp/env/jdbc/myds1"/>

<jee:jndi-lookup id="dataSource2" jndi-name="java:comp/env/jdbc/myds2"/>

<bean id="mySessionFactory1"

class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">

<list>

<value>product.hbm.xml</value>

</list>

</property>

<value>

hibernate.dialect=org.hibernate.dialect.MySQLDialect

hibernate.show_sql=true

</value>

</property>

</bean>

<bean id="mySessionFactory2"

class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">

<list>

<value>inventory.hbm.xml</value>

</list>

</property>

<value>

hibernate.dialect=org.hibernate.dialect.OracleDialect

</value>

</property>

</bean>

</bean>

</bean>

</bean>

<aop:config>

<aop:pointcut id="productServiceMethods"

expression="execution(* product.ProductService.(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/>

</aop:config>

<tx:advice id="txAdvice" transaction-manager="myTxManager">

<tx:attributes>

<tx:method name="increasePrice" propagation="REQUIRED"/>

<tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/>

<tx:method name="*" propagation="SUPPORTS" read-only="true"/>

</tx:attributes>

</tx:advice>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 411

Both HibernateTransactionManager and JtaTransactionManager allow for proper JVM-

level cache handling with Hibernate, without container-specific transaction manager lookup or a JCA

connector (if you are not using EJB to initiate transactions).

HibernateTransactionManager can export the Hibernate JDBC Connection to plain JDBC

access code, for a specific DataSource. This capability allows for high-level transaction demarcation

with mixed Hibernate and JDBC data access completely without JTA, if you are accessing only

one database. HibernateTransactionManager automatically exposes the Hibernate transaction

as a JDBC transaction if you have set up the passed-in SessionFactory with a DataSource

through the dataSource property of the LocalSessionFactoryBean class. Alternatively, you can

specify explicitly the DataSource for which the transactions are supposed to be exposed through the

dataSource property of the HibernateTransactionManager class.

Comparing container-managed and locally defined resources

You can switch between a container-managed JNDI SessionFactory and a locally defined one,

without having to change a single line of application code. Whether to keep resource definitions in the

container or locally within the application is mainly a matter of the transaction strategy that you use.

Compared to a Spring-defined local SessionFactory, a manually registered JNDI SessionFactory

does not provide any benefits. Deploying a SessionFactory through Hibernate’s JCA connector

provides the added value of participating in the Java EE server’s management infrastructure, but does

not add actual value beyond that.

Spring’s transaction support is not bound to a container. Configured with any strategy other than JTA,

transaction support also works in a stand-alone or test environment. Especially in the typical case of

single-database transactions, Spring’s single-resource local transaction support is a lightweight and

powerful alternative to JTA. When you use local EJB stateless session beans to drive transactions, you

depend both on an EJB container and JTA, even if you access only a single database, and only use

stateless session beans to provide declarative transactions through container-managed transactions.

Also, direct use of JTA programmatically requires a Java EE environment as well. JTA does not involve

only container dependencies in terms of JTA itself and of JNDI DataSource instances. For non-Spring,

JTA-driven Hibernate transactions, you have to use the Hibernate JCA connector, or extra Hibernate

transaction code with the TransactionManagerLookup configured for proper JVM-level caching.

Spring-driven transactions can work as well with a locally defined Hibernate SessionFactory as

they do with a local JDBC DataSource if they are accessing a single database. Thus you only have

to use Spring’s JTA transaction strategy when you have distributed transaction requirements. A JCA

connector requires container-specific deployment steps, and obviously JCA support in the first place.

This configuration requires more work than deploying a simple web application with local resource

definitions and Spring-driven transactions. Also, you often need the Enterprise Edition of your container

if you are using, for example, WebLogic Express, which does not provide JCA. A Spring application with

local resources and transactions spanning one single database works in any Java EE web container

(without JTA, JCA, or EJB) such as Tomcat, Resin, or even plain Jetty. Additionally, you can easily

reuse such a middle tier in desktop applications or test suites.

All things considered, if you do not use EJBs, stick with local SessionFactory setup and Spring’s

HibernateTransactionManager or JtaTransactionManager. You get all of the benefits,

including proper transactional JVM-level caching and distributed transactions, without the inconvenience

of container deployment. JNDI registration of a Hibernate SessionFactory through the JCA connector

only adds value when used in conjunction with EJBs.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 412

Spurious application server warnings with Hibernate

In some JTA environments with very strict XADataSource implementations — currently only some

WebLogic Server and WebSphere versions — when Hibernate is configured without regard to the JTA

PlatformTransactionManager object for that environment, it is possible for spurious warning or

exceptions to show up in the application server log. These warnings or exceptions indicate that the

connection being accessed is no longer valid, or JDBC access is no longer valid, possibly because the

transaction is no longer active. As an example, here is an actual exception from WebLogic:

java.sql.SQLException: The transaction is no longer active - status: Committed. No

further JDBC access is allowed within this transaction.

You resolve this warning by simply making Hibernate aware of the JTA

PlatformTransactionManager instance, to which it will synchronize (along with Spring). You have

two options for doing this:

• If in your application context you are already directly obtaining the

JTA PlatformTransactionManager object (presumably from JNDI through

JndiObjectFactoryBean or <jee:jndi-lookup>) and feeding it, for example, to Spring’s

JtaTransactionManager, then the easiest way is to specify a reference to the bean defining this

JTA PlatformTransactionManager instance as the value of the jtaTransactionManager

property for LocalSessionFactoryBean. Spring then makes the object available to Hibernate.

• More likely you do not already have the JTA PlatformTransactionManager instance, because

Spring’s JtaTransactionManager can find it itself. Thus you need to configure Hibernate to look

up JTA PlatformTransactionManager directly. You do this by configuring an application server-

specific TransactionManagerLookup class in the Hibernate configuration, as described in the

Hibernate manual.

The remainder of this section describes the sequence of events that occur with and without Hibernate’s

awareness of the JTA PlatformTransactionManager.

When Hibernate is not configured with any awareness of the JTA PlatformTransactionManager,

the following events occur when a JTA transaction commits:

• The JTA transaction commits.

• Spring’s JtaTransactionManager is synchronized to the JTA transaction, so it is called back

through an afterCompletion callback by the JTA transaction manager.

• Among other activities, this synchronization can trigger a callback by Spring to Hibernate, through

Hibernate’s afterTransactionCompletion callback (used to clear the Hibernate cache), followed

by an explicit close() call on the Hibernate Session, which causes Hibernate to attempt to close()

the JDBC Connection.

• In some environments, this Connection.close() call then triggers the warning or error, as the

application server no longer considers the Connection usable at all, because the transaction has

already been committed.

When Hibernate is configured with awareness of the JTA PlatformTransactionManager, the

following events occur when a JTA transaction commits:

• the JTA transaction is ready to commit.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 413

• Spring’s JtaTransactionManager is synchronized to the JTA transaction, so the transaction is

called back through a beforeCompletion callback by the JTA transaction manager.

• Spring is aware that Hibernate itself is synchronized to the JTA transaction, and behaves differently

than in the previous scenario. Assuming the Hibernate Session needs to be closed at all, Spring

will close it now.

• The JTA transaction commits.

• Hibernate is synchronized to the JTA transaction, so the transaction is called back through an

afterCompletion callback by the JTA transaction manager, and can properly clear its cache.

15.4 JDO

Spring supports the standard JDO 2.0 and 2.1 APIs as data access strategy, following the

same style as the Hibernate support. The corresponding integration classes reside in the

org.springframework.orm.jdo package.

PersistenceManagerFactory setup

Spring provides a LocalPersistenceManagerFactoryBean class that allows you to define a local

JDO PersistenceManagerFactory within a Spring application context:

<beans>

</bean>

</beans>

Alternatively, you can set up a PersistenceManagerFactory through direct instantiation of

a PersistenceManagerFactory implementation class. A JDO PersistenceManagerFactory

implementation class follows the JavaBeans pattern, just like a JDBC DataSource implementation

class, which is a natural fit for a configuration that uses Spring. This setup style usually supports a

Spring-defined JDBC DataSource, passed into the connectionFactory property. For example, for

the open source JDO implementation DataNucleus (formerly JPOX) ( http://www.datanucleus.org/), this

is the XML configuration of the PersistenceManagerFactory implementation:

<beans>

</bean>

</bean>

</beans>

You can also set up JDO PersistenceManagerFactory in the JNDI environment of a Java EE

application server, usually through the JCA connector provided by the particular JDO implementation.

Spring’s standard JndiObjectFactoryBean or <jee:jndi-lookup> can be used to retrieve and

expose such a PersistenceManagerFactory. However, outside an EJB context, no real benefit

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 414

exists in holding the PersistenceManagerFactory in JNDI: only choose such a setup for a good

reason. See the section called “Comparing container-managed and locally defined resources” for a

discussion; the arguments there apply to JDO as well.

Implementing DAOs based on the plain JDO API

DAOs can also be written directly against plain JDO API, without any Spring dependencies, by using

an injected PersistenceManagerFactory. The following is an example of a corresponding DAO

implementation:

public class ProductDaoImpl implements ProductDao {

private PersistenceManagerFactory persistenceManagerFactory;

public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {

this.persistenceManagerFactory = pmf;

}

public Collection loadProductsByCategory(String category) {

PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager();

try {

Query query = pm.newQuery(Product.class, "category = pCategory");

query.declareParameters("String pCategory");

return query.execute(category);

}

finally {

pm.close();

}

Because the above DAO follows the dependency injection pattern, it fits nicely into a Spring container,

just as it would if coded against Spring’s JdoTemplate:

<beans>

</bean>

</beans>

The main problem with such DAOs is that they always get a new PersistenceManager

from the factory. To access a Spring-managed transactional PersistenceManager, define a

TransactionAwarePersistenceManagerFactoryProxy (as included in Spring) in front of your

target PersistenceManagerFactory, then passing a reference to that proxy into your DAOs as in

the following example:

<beans>

<bean id="myPmfProxy"

class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy">

</bean>

</bean>

</beans>

Your data access code will receive a transactional PersistenceManager (if any) from

the PersistenceManagerFactory.getPersistenceManager() method that it calls. The

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 415

latter method call goes through the proxy, which first checks for a current transactional

PersistenceManager before getting a new one from the factory. Any close() calls on the

PersistenceManager are ignored in case of a transactional PersistenceManager.

If your data access code always runs within an active transaction (or at least within active transaction

synchronization), it is safe to omit the PersistenceManager.close() call and thus the entire

finally block, which you might do to keep your DAO implementations concise:

public class ProductDaoImpl implements ProductDao {

private PersistenceManagerFactory persistenceManagerFactory;

public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {

this.persistenceManagerFactory = pmf;

}

public Collection loadProductsByCategory(String category) {

PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager();

Query query = pm.newQuery(Product.class, "category = pCategory");

query.declareParameters("String pCategory");

return query.execute(category);

}

With such DAOs that rely on active transactions, it is recommended that you enforce active transactions

through turning off TransactionAwarePersistenceManagerFactoryProxy's allowCreate

flag:

<beans>

<bean id="myPmfProxy"

class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy">

</bean>

</bean>

</beans>

The main advantage of this DAO style is that it depends on JDO API only; no import of any Spring

class is required. This is of course appealing from a non-invasiveness perspective, and might feel more

natural to JDO developers.

However, the DAO throws plain JDOException (which is unchecked, so does not have to be declared

or caught), which means that callers can only treat exceptions as fatal, unless you want to depend on

JDO’s own exception structure. Catching specific causes such as an optimistic locking failure is not

possible without tying the caller to the implementation strategy. This trade off might be acceptable to

applications that are strongly JDO-based and/or do not need any special exception treatment.

In summary, you can DAOs based on the plain JDO API, and they can still participate in Spring-

managed transactions. This strategy might appeal to you if you are already familiar with JDO.

However, such DAOs throw plain JDOException, and you would have to convert explicitly to Spring’s

DataAccessException (if desired).

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 416

Transaction management

Note

You are strongly encouraged to read Section 12.5, “Declarative transaction management” if you

have not done so, to get a more detailed coverage of Spring’s declarative transaction support.

To execute service operations within transactions, you can use Spring’s common declarative transaction

facilities. For example:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

</bean>

</bean>

<tx:advice id="txAdvice" transaction-manager="txManager">

<tx:attributes>

<tx:method name="increasePrice*" propagation="REQUIRED"/>

<tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/>

<tx:method name="" propagation="SUPPORTS" read-only="true"/>

</tx:attributes>

</tx:advice>

<aop:config>

<aop:pointcut id="productServiceMethods"

expression="execution( product.ProductService.*(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/>

</aop:config>

</beans>

JDO requires an active transaction to modify a persistent object. The non-transactional flush concept

does not exist in JDO, in contrast to Hibernate. For this reason, you need to set up the chosen

JDO implementation for a specific environment. Specifically, you need to set it up explicitly for JTA

synchronization, to detect an active JTA transaction itself. This is not necessary for local transactions

as performed by Spring’s JdoTransactionManager, but it is necessary to participate in JTA

transactions, whether driven by Spring’s JtaTransactionManager or by EJB CMT and plain JTA.

JdoTransactionManager is capable of exposing a JDO transaction to JDBC access code that

accesses the same JDBC DataSource, provided that the registered JdoDialect supports retrieval

of the underlying JDBC Connection. This is the case for JDBC-based JDO 2.0 implementations by

default.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 417

JdoDialect

As an advanced feature, both JdoTemplate and JdoTransactionManager support a custom

JdoDialect that can be passed into the jdoDialect bean property. In this scenario, the DAOs

will not receive a PersistenceManagerFactory reference but rather a full JdoTemplate instance

(for example, passed into the jdoTemplate property of JdoDaoSupport). Using a JdoDialect

implementation, you can enable advanced features supported by Spring, usually in a vendor-specific

manner:

• Applying specific transaction semantics such as custom isolation level or transaction timeout

• Retrieving the transactional JDBC Connection for exposure to JDBC-based DAOs

• Applying query timeouts, which are automatically calculated from Spring-managed transaction

timeouts

• Eagerly flushing a PersistenceManager, to make transactional changes visible to JDBC-based

data access code

• Advanced translation of JDOExceptions to Spring DataAccessExceptions

See the JdoDialect javadocs for more details on its operations and how to use them within Spring’s

JDO support.

15.5 JPA

The Spring JPA, available under the org.springframework.orm.jpa package, offers

comprehensive support for the Java Persistence API in a similar manner to the integration with Hibernate

or JDO, while being aware of the underlying implementation in order to provide additional features.

Three options for JPA setup in a Spring environment

The Spring JPA support offers three ways of setting up the JPA EntityManagerFactory that will be

used by the application to obtain an entity manager.

LocalEntityManagerFactoryBean

Note

Only use this option in simple deployment environments such as stand-alone applications and

integration tests.

The LocalEntityManagerFactoryBean creates an EntityManagerFactory suitable for simple

deployment environments where the application uses only JPA for data access. The factory bean

uses the JPA PersistenceProvider autodetection mechanism (according to JPA’s Java SE

bootstrapping) and, in most cases, requires you to specify only the persistence unit name:

<beans>

</bean>

</beans>

This form of JPA deployment is the simplest and the most limited. You cannot refer to an existing JDBC

DataSource bean definition and no support for global transactions exists. Furthermore, weaving (byte-

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 418

code transformation) of persistent classes is provider-specific, often requiring a specific JVM agent to

specified on startup. This option is sufficient only for stand-alone applications and test environments,

for which the JPA specification is designed.

Obtaining an EntityManagerFactory from JNDI

Note

Use this option when deploying to a Java EE 5 server. Check your server’s documentation on

how to deploy a custom JPA provider into your server, allowing for a different provider than the

server’s default.

Obtaining an EntityManagerFactory from JNDI (for example in a Java EE 5 environment), is simply

a matter of changing the XML configuration:

<beans>

<jee:jndi-lookup id="myEmf" jndi-name="persistence/myPersistenceUnit"/>

</beans>

This action assumes standard Java EE 5 bootstrapping: the Java EE server autodetects persistence

units (in effect, META-INF/persistence.xml files in application jars) and persistence-unit-ref

entries in the Java EE deployment descriptor (for example, web.xml) and defines environment naming

context locations for those persistence units.

In such a scenario, the entire persistence unit deployment, including the weaving (byte-code

transformation) of persistent classes, is up to the Java EE server. The JDBC DataSource

is defined through a JNDI location in the META-INF/persistence.xml file; EntityManager

transactions are integrated with the server’s JTA subsystem. Spring merely uses the obtained

EntityManagerFactory, passing it on to application objects through dependency injection, and

managing transactions for the persistence unit, typically through JtaTransactionManager.

If multiple persistence units are used in the same application, the bean names of such JNDI-retrieved

persistence units should match the persistence unit names that the application uses to refer to them,

for example, in @PersistenceUnit and @PersistenceContext annotations.

LocalContainerEntityManagerFactoryBean

Note

Use this option for full JPA capabilities in a Spring-based application environment. This includes

web containers such as Tomcat as well as stand-alone applications and integration tests with

sophisticated persistence requirements.

The LocalContainerEntityManagerFactoryBean gives full control over

EntityManagerFactory configuration and is appropriate for environments where fine-

grained customization is required. The LocalContainerEntityManagerFactoryBean creates

a PersistenceUnitInfo instance based on the persistence.xml file, the supplied

dataSourceLookup strategy, and the specified loadTimeWeaver. It is thus possible to work with

custom data sources outside of JNDI and to control the weaving process. The following example shows

a typical bean definition for a LocalContainerEntityManagerFactoryBean:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 419

<beans>

</property>

</bean>

</beans>

The following example shows a typical persistence.xml file:

<persistence-unit name="myUnit" transaction-type="RESOURCE_LOCAL">

<mapping-file>META-INF/orm.xml</mapping-file>

<exclude-unlisted-classes/>

</persistence-unit>

</persistence>

Note

The exclude-unlisted-classes element always indicates that no scanning for annotated

entity classes is supposed to occur, in order to support the <exclude-unlisted-classes/>

shortcut. This is in line with the JPA specification, which suggests that shortcut, but unfortunately

is in conflict with the JPA XSD, which implies false for that shortcut. Consequently, <exclude-

unlisted-classes> false </exclude-unlisted-classes/> is not supported. Simply

omit the exclude-unlisted-classes element if you want entity class scanning to occur.

Using the LocalContainerEntityManagerFactoryBean is the most powerful JPA setup option,

allowing for flexible local configuration within the application. It supports links to an existing JDBC

DataSource, supports both local and global transactions, and so on. However, it also imposes

requirements on the runtime environment, such as the availability of a weaving-capable class loader if

the persistence provider demands byte-code transformation.

This option may conflict with the built-in JPA capabilities of a Java EE 5 server. In a full Java EE

5 environment, consider obtaining your EntityManagerFactory from JNDI. Alternatively, specify

a custom persistenceXmlLocation on your LocalContainerEntityManagerFactoryBean

definition, for example, META-INF/my-persistence.xml, and only include a descriptor with that name

in your application jar files. Because the Java EE 5 server only looks for default META-INF/

persistence.xml files, it ignores such custom persistence units and hence avoid conflicts with a

Spring-driven JPA setup upfront. (This applies to Resin 3.1, for example.)

When is load-time weaving required?

Not all JPA providers require a JVM agent ; Hibernate is an example of one that does not. If your

provider does not require an agent or you have other alternatives, such as applying enhancements

at build time through a custom compiler or an ant task, the load-time weaver should not be used.

The LoadTimeWeaver interface is a Spring-provided class that allows JPA ClassTransformer

instances to be plugged in a specific manner, depending whether the environment is a web container

or application server. Hooking ClassTransformers through an agent typically is not efficient. The

agents work against the entire virtual machine and inspect every class that is loaded, which is usually

undesirable in a production server environment.

Spring provides a number of LoadTimeWeaver implementations for various environments, allowing

ClassTransformer instances to be applied only per class loader and not per VM.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 420

Refer to the section called “Spring configuration” in the AOP chapter for more insight regarding the

LoadTimeWeaver implementations and their setup, either generic or customized to various platforms

(such as Tomcat, WebLogic, GlassFish, Resin and JBoss).

As described in the aforementioned section, you can configure a context-wide LoadTimeWeaver

using the @EnableLoadTimeWeaving annotation of context:load-time-weaver XML element.

Such a global weaver is picked up by all JPA LocalContainerEntityManagerFactoryBeans

automatically. This is the preferred way of setting up a load-time weaver, delivering autodetection of the

platform (WebLogic, GlassFish, Tomcat, Resin, JBoss or VM agent) and automatic propagation of the

weaver to all weaver-aware beans:

<context:load-time-weaver/>

...

</bean>

However, if needed, one can manually specify a dedicated weaver through the loadTimeWeaver

property:

</property>

</bean>

No matter how the LTW is configured, using this technique, JPA applications relying on instrumentation

can run in the target platform (ex: Tomcat) without needing an agent. This is important especially when

the hosting applications rely on different JPA implementations because the JPA transformers are applied

only at class loader level and thus are isolated from each other.

Dealing with multiple persistence units

For applications that rely on multiple persistence units locations, stored in various JARS in the classpath,

for example, Spring offers the PersistenceUnitManager to act as a central repository and to avoid

the persistence units discovery process, which can be expensive. The default implementation allows

multiple locations to be specified that are parsed and later retrieved through the persistence unit name.

(By default, the classpath is searched for META-INF/persistence.xml files.)

<list>

<value>org/springframework/orm/jpa/domain/persistence-multi.xml</value>

<value>classpath:/my/package/*/custom-persistence.xml</value>

<value>classpath:META-INF/persistence.xml</value>

</list>

</property>

<map>

</map>

</property>

</bean>

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 421

The default implementation allows customization of the PersistenceUnitInfo instances, before

they are fed to the JPA provider, declaratively through its properties, which affect all hosted units,

or programmatically, through the PersistenceUnitPostProcessor, which allows persistence unit

selection. If no PersistenceUnitManager is specified, one is created and used internally by

LocalContainerEntityManagerFactoryBean.

Implementing DAOs based on plain JPA

Note

Although EntityManagerFactory instances are thread-safe, EntityManager instances are

not. The injected JPA EntityManager behaves like an EntityManager fetched from an

application server’s JNDI environment, as defined by the JPA specification. It delegates all calls

to the current transactional EntityManager, if any; otherwise, it falls back to a newly created

EntityManager per operation, in effect making its usage thread-safe.

It is possible to write code against the plain JPA without any Spring dependencies,

by using an injected EntityManagerFactory or EntityManager. Spring can understand

@PersistenceUnit and @PersistenceContext annotations both at field and method level if a

PersistenceAnnotationBeanPostProcessor is enabled. A plain JPA DAO implementation using

the @PersistenceUnit annotation might look like this:

public class ProductDaoImpl implements ProductDao {

private EntityManagerFactory emf;

@PersistenceUnit

public void setEntityManagerFactory(EntityManagerFactory emf) {

this.emf = emf;

}

public Collection loadProductsByCategory(String category) {

EntityManager em = this.emf.createEntityManager();

try {

Query query = em.createQuery("from Product as p where p.category = ?1");

query.setParameter(1, category);

return query.getResultList();

}

finally {

if (em != null) {

em.close();

}

The DAO above has no dependency on Spring and still fits nicely into a Spring application

context. Moreover, the DAO takes advantage of annotations to require the injection of the default

EntityManagerFactory:

<beans>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 422

As an alternative to defining a PersistenceAnnotationBeanPostProcessor explicitly, consider

using the Spring context:annotation-config XML element in your application context

configuration. Doing so automatically registers all Spring standard post-processors for annotation-based

configuration, including CommonAnnotationBeanPostProcessor and so on.

<beans>

<context:annotation-config/>

</beans>

The main problem with such a DAO is that it always creates a new EntityManager through the factory.

You can avoid this by requesting a transactional EntityManager (also called "shared EntityManager"

because it is a shared, thread-safe proxy for the actual transactional EntityManager) to be injected

instead of the factory:

public class ProductDaoImpl implements ProductDao {

@PersistenceContext

private EntityManager em;

public Collection loadProductsByCategory(String category) {

Query query = em.createQuery("from Product as p where p.category = :category");

query.setParameter("category", category);

return query.getResultList();

}

The @PersistenceContext annotation has an optional attribute type, which defaults to

PersistenceContextType.TRANSACTION. This default is what you need to receive a shared

EntityManager proxy. The alternative, PersistenceContextType.EXTENDED, is a completely

different affair: This results in a so-called extended EntityManager, which is not thread-safe and hence

must not be used in a concurrently accessed component such as a Spring-managed singleton bean.

Extended EntityManagers are only supposed to be used in stateful components that, for example, reside

in a session, with the lifecycle of the EntityManager not tied to a current transaction but rather being

completely up to the application.

Method- and field-level Injection

Annotations that indicate dependency injections (such as @PersistenceUnit and

@PersistenceContext) can be applied on field or methods inside a class, hence the

expressions method-level injection and field-level injection. Field-level annotations are concise

and easier to use while method-level allows for further processing of the injected dependency. In

both cases the member visibility (public, protected, private) does not matter.

What about class-level annotations?

On the Java EE 5 platform, they are used for dependency declaration and not for resource injection.

The injected EntityManager is Spring-managed (aware of the ongoing transaction). It is important to

note that even though the new DAO implementation uses method level injection of an EntityManager

instead of an EntityManagerFactory, no change is required in the application context XML due to

annotation usage.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 423

The main advantage of this DAO style is that it only depends on Java Persistence API; no import of any

Spring class is required. Moreover, as the JPA annotations are understood, the injections are applied

automatically by the Spring container. This is appealing from a non-invasiveness perspective, and might

feel more natural to JPA developers.

Transaction Management

Note

You are strongly encouraged to read Section 12.5, “Declarative transaction management” if you

have not done so, to get a more detailed coverage of Spring’s declarative transaction support.

To execute service operations within transactions, you can use Spring’s common declarative transaction

facilities. For example:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/tx

http://www.springframework.org/schema/tx/spring-tx.xsd

http://www.springframework.org/schema/aop

http://www.springframework.org/schema/aop/spring-aop.xsd">

</bean>

</bean>

<aop:config>

<aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.(..))"/>

<aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/>

</aop:config>

<tx:advice id="txAdvice" transaction-manager="myTxManager">

<tx:attributes>

<tx:method name="increasePrice" propagation="REQUIRED"/>

<tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/>

<tx:method name="*" propagation="SUPPORTS" read-only="true"/>

</tx:attributes>

</tx:advice>

</beans>

Spring JPA allows a configured JpaTransactionManager to expose a JPA transaction to JDBC

access code that accesses the same JDBC DataSource, provided that the registered JpaDialect

supports retrieval of the underlying JDBC Connection. Out of the box, Spring provides dialects for

the Toplink, Hibernate and OpenJPA JPA implementations. See the next section for details on the

JpaDialect mechanism.

JpaDialect

As an advanced feature JpaTemplate, JpaTransactionManager and subclasses of

AbstractEntityManagerFactoryBean support a custom JpaDialect, to be passed into the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 424

jpaDialect bean property. In such a scenario, the DAOs do not receive an EntityManagerFactory

reference but rather a full JpaTemplate instance (for example, passed into the jpaTemplate property

of JpaDaoSupport). A JpaDialect implementation can enable some advanced features supported

by Spring, usually in a vendor-specific manner:

• Applying specific transaction semantics such as custom isolation level or transaction timeout)

• Retrieving the transactional JDBC Connection for exposure to JDBC-based DAOs)

• Advanced translation of PersistenceExceptions to Spring DataAccessExceptions

This is particularly valuable for special transaction semantics and for advanced translation of exception.

The default implementation used ( DefaultJpaDialect) does not provide any special capabilities

and if the above features are required, you have to specify the appropriate dialect.

See the JpaDialect javadocs for more details of its operations and how they are used within Spring’s

JPA support.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 425

16. Marshalling XML using O/X Mappers

16.1 Introduction

In this chapter, we will describe Spring’s Object/XML Mapping support. Object/XML Mapping, or O/X

mapping for short, is the act of converting an XML document to and from an object. This conversion

process is also known as XML Marshalling, or XML Serialization. This chapter uses these terms

interchangeably.

Within the field of O/X mapping, a marshaller is responsible for serializing an object (graph) to XML. In

similar fashion, an unmarshaller deserializes the XML to an object graph. This XML can take the form

of a DOM document, an input or output stream, or a SAX handler.

Some of the benefits of using Spring for your O/X mapping needs are:

Ease of configuration

Spring’s bean factory makes it easy to configure marshallers, without needing to construct JAXB context,

JiBX binding factories, etc. The marshallers can be configured as any other bean in your application

context. Additionally, XML Schema-based configuration is available for a number of marshallers, making

the configuration even simpler.

Consistent Interfaces

Spring’s O/X mapping operates through two global interfaces: the Marshaller and Unmarshaller

interface. These abstractions allow you to switch O/X mapping frameworks with relative ease, with little

or no changes required on the classes that do the marshalling. This approach has the additional benefit

of making it possible to do XML marshalling with a mix-and-match approach (e.g. some marshalling

performed using JAXB, other using XMLBeans) in a non-intrusive fashion, leveraging the strength of

each technology.

Consistent Exception Hierarchy

Spring provides a conversion from exceptions from the underlying O/X mapping tool to its own exception

hierarchy with the XmlMappingException as the root exception. As can be expected, these runtime

exceptions wrap the original exception so no information is lost.

16.2 Marshaller and Unmarshaller

As stated in the introduction, a marshaller serializes an object to XML, and an unmarshaller deserializes

XML stream to an object. In this section, we will describe the two Spring interfaces used for this purpose.

Marshaller

Spring abstracts all marshalling operations behind the org.springframework.oxm.Marshaller

interface, the main methods of which is listed below.

public interface Marshaller {

/**

* Marshals the object graph with the given root into the provided Result.

void marshal(Object graph, Result result) throws XmlMappingException, IOException;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 426

The Marshaller interface has one main method, which marshals the given object to a given

javax.xml.transform.Result. Result is a tagging interface that basically represents an XML

output abstraction: concrete implementations wrap various XML representations, as indicated in the

table below.

Result implementation Wraps XML representation

DOMResult org.w3c.dom.Node

SAXResult org.xml.sax.ContentHandler

StreamResult java.io.File, java.io.OutputStream, or

java.io.Writer

Note

Although the marshal() method accepts a plain object as its first parameter, most Marshaller

implementations cannot handle arbitrary objects. Instead, an object class must be mapped in a

mapping file, marked with an annotation, registered with the marshaller, or have a common base

class. Refer to the further sections in this chapter to determine how your O/X technology of choice

manages this.

Unmarshaller

Similar to the Marshaller, there is the org.springframework.oxm.Unmarshaller interface.

public interface Unmarshaller {

/**

* Unmarshals the given provided Source into an object graph.

Object unmarshal(Source source) throws XmlMappingException, IOException;

}

This interface also has one method, which reads from the given javax.xml.transform.Source (an

XML input abstraction), and returns the object read. As with Result, Source is a tagging interface that

has three concrete implementations. Each wraps a different XML representation, as indicated in the

table below.

Source implementation Wraps XML representation

DOMSource org.w3c.dom.Node

SAXSource org.xml.sax.InputSource, and

org.xml.sax.XMLReader

StreamSource java.io.File, java.io.InputStream, or

java.io.Reader

Even though there are two separate marshalling interfaces ( Marshaller and Unmarshaller),

all implementations found in Spring-WS implement both in one class. This means that you can

wire up one marshaller class and refer to it both as a marshaller and an unmarshaller in your

applicationContext.xml.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 427

XmlMappingException

Spring converts exceptions from the underlying O/X mapping tool to its own exception hierarchy with the

XmlMappingException as the root exception. As can be expected, these runtime exceptions wrap

the original exception so no information will be lost.

Additionally, the MarshallingFailureException and UnmarshallingFailureException

provide a distinction between marshalling and unmarshalling operations, even though the underlying

O/X mapping tool does not do so.

The O/X Mapping exception hierarchy is shown in the following figure: image::images/oxm-

exceptions.png[width=400]

O/X Mapping exception hierarchy

16.3 Using Marshaller and Unmarshaller

Spring’s OXM can be used for a wide variety of situations. In the following example, we will use it to

marshal the settings of a Spring-managed application as an XML file. We will use a simple JavaBean

to represent the settings:

public class Settings {

private boolean fooEnabled;

public boolean isFooEnabled() {

return fooEnabled;

}

public void setFooEnabled(boolean fooEnabled) {

this.fooEnabled = fooEnabled;

}

The application class uses this bean to store its settings. Besides a main method, the class has

two methods: saveSettings() saves the settings bean to a file named settings.xml, and

loadSettings() loads these settings again. A main() method constructs a Spring application

context, and calls these two methods.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 428

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import javax.xml.transform.stream.StreamResult;

import javax.xml.transform.stream.StreamSource;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import org.springframework.oxm.Marshaller;

import org.springframework.oxm.Unmarshaller;

public class Application {

private static final String FILE_NAME = "settings.xml";

private Settings settings = new Settings();

private Marshaller marshaller;

private Unmarshaller unmarshaller;

public void setMarshaller(Marshaller marshaller) {

this.marshaller = marshaller;

}

public void setUnmarshaller(Unmarshaller unmarshaller) {

this.unmarshaller = unmarshaller;

}

public void saveSettings() throws IOException {

FileOutputStream os = null;

try {

os = new FileOutputStream(FILE_NAME);

this.marshaller.marshal(settings, new StreamResult(os));

} finally {

if (os != null) {

os.close();

}

public void loadSettings() throws IOException {

FileInputStream is = null;

try {

is = new FileInputStream(FILE_NAME);

this.settings = (Settings) this.unmarshaller.unmarshal(new StreamSource(is));

} finally {

if (is != null) {

is.close();

}

public static void main(String[] args) throws IOException {

ApplicationContext appContext =

new ClassPathXmlApplicationContext("applicationContext.xml");

Application application = (Application) appContext.getBean("application");

application.saveSettings();

application.loadSettings();

}

The Application requires both a marshaller and unmarshaller property to be set. We can do

so using the following applicationContext.xml:

<beans>

</bean>

</beans>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 429

This application context uses Castor, but we could have used any of the other marshaller instances

described later in this chapter. Note that Castor does not require any further configuration by default,

so the bean definition is rather simple. Also note that the CastorMarshaller implements both

Marshaller and Unmarshaller, so we can refer to the castorMarshaller bean in both the

marshaller and unmarshaller property of the application.

This sample application produces the following settings.xml file:

<?xml version="1.0" encoding="UTF-8"?>

16.4 XML Schema-based Configuration

Marshallers could be configured more concisely using tags from the OXM namespace. To make

these tags available, the appropriate schema has to be referenced first in the preamble of the XML

configuration file. Note the oxm related text below:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:oxm="http://www.springframework.org/schema/oxm" xsi:schemaLocation="http://

www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-

beans.xsd http://www.springframework.org/schema/oxm http://www.springframework.org/schema/oxm/spring-

oxm.xsd">

Currently, the following tags are available:

•jaxb2-marshaller

•xmlbeans-marshaller

•castor-marshaller

•jibx-marshaller

Each tag will be explained in its respective marshaller’s section. As an example though, here is how the

configuration of a JAXB2 marshaller might look like:

<oxm:jaxb2-marshaller id="marshaller" contextPath="org.springframework.ws.samples.airline.schema"/>

16.5 JAXB

The JAXB binding compiler translates a W3C XML Schema into one or more Java classes, a

jaxb.properties file, and possibly some resource files. JAXB also offers a way to generate a schema

from annotated Java classes.

Spring supports the JAXB 2.0 API as XML marshalling strategies, following the Marshaller

and Unmarshaller interfaces described in Section 16.2, “Marshaller and Unmarshaller”. The

corresponding integration classes reside in the org.springframework.oxm.jaxb package.

Jaxb2Marshaller

The Jaxb2Marshaller class implements both the Spring Marshaller and Unmarshaller

interface. It requires a context path to operate, which you can set using the contextPath property. The

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 430

context path is a list of colon (:) separated Java package names that contain schema derived classes. It

also offers a classesToBeBound property, which allows you to set an array of classes to be supported

by the marshaller. Schema validation is performed by specifying one or more schema resource to the

bean, like so:

<beans>

<list>

<value>org.springframework.oxm.jaxb.Flight</value>

<value>org.springframework.oxm.jaxb.Flights</value>

</list>

</property>

</bean>

...

</beans>

XML Schema-based Configuration

The jaxb2-marshaller tag configures a

org.springframework.oxm.jaxb.Jaxb2Marshaller. Here is an example:

<oxm:jaxb2-marshaller id="marshaller" contextPath="org.springframework.ws.samples.airline.schema"/>

Alternatively, the list of classes to bind can be provided to the marshaller via the class-to-be-bound

child tag:

<oxm:jaxb2-marshaller id="marshaller">

<oxm:class-to-be-bound name="org.springframework.ws.samples.airline.schema.Airport"/>

<oxm:class-to-be-bound name="org.springframework.ws.samples.airline.schema.Flight"/>

...

</oxm:jaxb2-marshaller>

Available attributes are:

Attribute Description Required

id the id of the marshaller no

contextPath the JAXB Context path no

16.6 Castor

Castor XML mapping is an open source XML binding framework. It allows you to transform the data

contained in a java object model into/from an XML document. By default, it does not require any further

configuration, though a mapping file can be used to have more control over the behavior of Castor.

For more information on Castor, refer to the Castor web site. The Spring integration classes reside in

the org.springframework.oxm.castor package.

CastorMarshaller

As with JAXB, the CastorMarshaller implements both the Marshaller and Unmarshaller

interface. It can be wired up as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 431

<beans>

...

</beans>

Mapping

Although it is possible to rely on Castor’s default marshalling behavior, it might be necessary to have

more control over it. This can be accomplished using a Castor mapping file. For more information, refer

to Castor XML Mapping.

The mapping can be set using the mappingLocation resource property, indicated below with a

classpath resource.

<beans>

</bean>

</beans>

XML Schema-based Configuration

The castor-marshaller tag configures a

org.springframework.oxm.castor.CastorMarshaller. Here is an example:

<oxm:castor-marshaller id="marshaller" mapping-location="classpath:org/springframework/oxm/castor/

mapping.xml"/>

The marshaller instance can be configured in two ways, by specifying either the location of a mapping

file (through the mapping-location property), or by identifying Java POJOs (through the target-

class or target-package properties) for which there exist corresponding XML descriptor classes.

The latter way is usually used in conjunction with XML code generation from XML schemas.

Available attributes are:

Attribute Description Required

id the id of the marshaller no

encoding the encoding to use for

unmarshalling from XML

target-class a Java class name for a

POJO for which an XML

class descriptor is available

(as generated through code

generation)

target-package a Java package name

that identifies a package

that contains POJOs and

their corresponding Castor

XML descriptor classes (as

generated through code

generation from XML schemas)

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 432

Attribute Description Required

mapping-location location of a Castor XML

mapping file

16.7 XMLBeans

XMLBeans is an XML binding tool that has full XML Schema support, and offers full XML Infoset fidelity.

It takes a different approach to that of most other O/X mapping frameworks, in that all classes that are

generated from an XML Schema are all derived from XmlObject, and contain XML binding information

in them.

For more information on XMLBeans, refer to the XMLBeans web site . The Spring-WS integration

classes reside in the org.springframework.oxm.xmlbeans package.

XmlBeansMarshaller

The XmlBeansMarshaller implements both the Marshaller and Unmarshaller interfaces. It can

be configured as follows:

<beans>

...

</beans>

Note

Note that the XmlBeansMarshaller can only marshal objects of type XmlObject, and not

every java.lang.Object.

XML Schema-based Configuration

The xmlbeans-marshaller tag configures a

org.springframework.oxm.xmlbeans.XmlBeansMarshaller. Here is an example:

<oxm:xmlbeans-marshaller id="marshaller"/>

Available attributes are:

Attribute Description Required

id the id of the marshaller no

options the bean name of the

XmlOptions that is to be used

for this marshaller. Typically a

XmlOptionsFactoryBean

definition

16.8 JiBX

The JiBX framework offers a solution similar to that which JDO provides for ORM: a binding definition

defines the rules for how your Java objects are converted to or from XML. After preparing the binding

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 433

and compiling the classes, a JiBX binding compiler enhances the class files, and adds code to handle

converting instances of the classes from or to XML.

For more information on JiBX, refer to the JiBX web site. The Spring integration classes reside in the

org.springframework.oxm.jibx package.

JibxMarshaller

The JibxMarshaller class implements both the Marshaller and Unmarshaller interface. To

operate, it requires the name of the class to marshal in, which you can set using the targetClass

property. Optionally, you can set the binding name using the bindingName property. In the next sample,

we bind the Flights class:

<beans>

<property name="targetClass">org.springframework.oxm.jibx.Flights</property>

</bean>

...

</beans>

A JibxMarshaller is configured for a single class. If you want to marshal multiple classes, you have

to configure multiple JibxMarshallers with different targetClass property values.

XML Schema-based Configuration

The jibx-marshaller tag configures a org.springframework.oxm.jibx.JibxMarshaller.

Here is an example:

<oxm:jibx-marshaller id="marshaller" target-

class="org.springframework.ws.samples.airline.schema.Flight"/>

Available attributes are:

Attribute Description Required

id the id of the marshaller no

target-class the target class for this

marshaller

yes

bindingName the binding name used by this

marshaller

16.9 XStream

XStream is a simple library to serialize objects to XML and back again. It does not require any mapping,

and generates clean XML.

For more information on XStream, refer to the XStream web site. The Spring integration classes reside

in the org.springframework.oxm.xstream package.

XStreamMarshaller

The XStreamMarshaller does not require any configuration, and can be configured in an application

context directly. To further customize the XML, you can set analias map, which consists of string aliases

mapped to classes:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 434

<beans>

<props>

<prop key="Flight">org.springframework.oxm.xstream.Flight</prop>

</props>

</property>

</bean>

...

</beans>

Warning

By default, XStream allows for arbitrary classes to be unmarshalled, which can result in security

vulnerabilities. As such, it is not recommended to use the XStreamMarshaller to unmarshal

XML from external sources (i.e. the Web), as this can result in security vulnerabilities. If

you do use the XStreamMarshaller to unmarshal XML from an external source, set the

supportedClasses property on the XStreamMarshaller, like so:

...

</bean>

This will make sure that only the registered classes are eligible for unmarshalling.

Additionally, you can register custom converters to make sure that only your supported classes

can be unmarshalled. You might want to add a CatchAllConverter as the last converter in the

list, in addition to converters that explicitly support the domain classes that should be supported.

As a result, default XStream converters with lower priorities and possible security vulnerabilities

do not get invoked.

Note

Note that XStream is an XML serialization library, not a data binding library. Therefore, it has

limited namespace support. As such, it is rather unsuitable for usage within Web services.

Part V. The Web

This part of the reference documentation covers Spring Framework’s support for the presentation tier

(and specifically web-based presentation tiers) including support for WebSocket-style messaging in web

applications.

Spring Framework’s own web framework, Spring Web MVC, is covered in the first couple of chapters.

Subsequent chapters are concerned with Spring Framework’s integration with other web technologies,

such as JSF and.

Following that is coverage of Spring Framework’s MVC portlet framework.

The section then concludes with comprehensive coverage of the Spring Framework Chapter 21,

WebSocket Support (including Section 21.4, “STOMP Over WebSocket Messaging Architecture”).

• Chapter 17, Web MVC framework

• Chapter 18, View technologies

• Chapter 19, Integrating with other web frameworks

• Chapter 20, Portlet MVC Framework

• Chapter 21, WebSocket Support

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 436

17. Web MVC framework

17.1 Introduction to Spring Web MVC framework

The Spring Web model-view-controller (MVC) framework is designed around a DispatcherServlet

that dispatches requests to handlers, with configurable handler mappings, view resolution, locale, time

zone and theme resolution as well as support for uploading files. The default handler is based on the

@Controller and @RequestMapping annotations, offering a wide range of flexible handling methods.

With the introduction of Spring 3.0, the @Controller mechanism also allows you to create RESTful

Web sites and applications, through the @PathVariable annotation and other features.

"Open for extension…" A key design principle in Spring Web MVC and in Spring in general is the

"Open for extension, closed for modification" principle.

Some methods in the core classes of Spring Web MVC are marked final. As a developer you

cannot override these methods to supply your own behavior. This has not been done arbitrarily,

but specifically with this principle in mind.

For an explanation of this principle, refer to Expert Spring Web MVC and Web Flow by Seth

Ladd and others; specifically see the section "A Look At Design," on page 117 of the first edition.

Alternatively, see

•Bob Martin, The Open-Closed Principle (PDF)

You cannot add advice to final methods when you use Spring MVC. For example, you cannot

add advice to the AbstractController.setSynchronizeOnSession() method. Refer to

the section called “Understanding AOP proxies” for more information on AOP proxies and why

you cannot add advice to final methods.

In Spring Web MVC you can use any object as a command or form-backing object; you do not need

to implement a framework-specific interface or base class. Spring’s data binding is highly flexible: for

example, it treats type mismatches as validation errors that can be evaluated by the application, not as

system errors. Thus you need not duplicate your business objects' properties as simple, untyped strings

in your form objects simply to handle invalid submissions, or to convert the Strings properly. Instead, it

is often preferable to bind directly to your business objects.

Spring’s view resolution is extremely flexible. A Controller is typically responsible for preparing

a model Map with data and selecting a view name but it can also write directly to the response

stream and complete the request. View name resolution is highly configurable through file extension

or Accept header content type negotiation, through bean names, a properties file, or even a custom

ViewResolver implementation. The model (the M in MVC) is a Map interface, which allows for the

complete abstraction of the view technology. You can integrate directly with template based rendering

technologies such as JSP, Velocity and Freemarker, or directly generate XML, JSON, Atom, and many

other types of content. The model Map is simply transformed into an appropriate format, such as JSP

request attributes, a Velocity template model.

Features of Spring Web MVC

Spring Web Flow

Spring Web Flow (SWF) aims to be the best solution for the management of web application page

flow.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 437

SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and

Portlet environments. If you have a business process (or processes) that would benefit from a

conversational model as opposed to a purely request model, then SWF may be the solution.

SWF allows you to capture logical page flows as self-contained modules that are reusable in

different situations, and as such is ideal for building web application modules that guide the user

through controlled navigations that drive business processes.

For more information about SWF, consult the Spring Web Flow website.

Spring’s web module includes many unique web support features:

•Clear separation of roles. Each role — controller, validator, command object, form object, model

object, DispatcherServlet, handler mapping, view resolver, and so on — can be fulfilled by a

specialized object.

•Powerful and straightforward configuration of both framework and application classes as JavaBeans.

This configuration capability includes easy referencing across contexts, such as from web controllers

to business objects and validators.

•Adaptability, non-intrusiveness, and flexibility. Define any controller method signature you need,

possibly using one of the parameter annotations (such as @RequestParam, @RequestHeader,

@PathVariable, and more) for a given scenario.

•Reusable business code, no need for duplication. Use existing business objects as command or form

objects instead of mirroring them to extend a particular framework base class.

•Customizable binding and validation. Type mismatches as application-level validation errors that keep

the offending value, localized date and number binding, and so on instead of String-only form objects

with manual parsing and conversion to business objects.

•Customizable handler mapping and view resolution. Handler mapping and view resolution strategies

range from simple URL-based configuration, to sophisticated, purpose-built resolution strategies.

Spring is more flexible than web MVC frameworks that mandate a particular technique.

•Flexible model transfer. Model transfer with a name/value Map supports easy integration with any

view technology.

•Customizable locale, time zone and theme resolution, support for JSPs with or without Spring tag

library, support for JSTL, support for Velocity without the need for extra bridges, and so on.

•A simple yet powerful JSP tag library known as the Spring tag library that provides support for features

such as data binding and themes. The custom tags allow for maximum flexibility in terms of markup

code. For information on the tag library descriptor, see the appendix entitled Chapter 36, spring.tld

•A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP pages much easier.

For information on the tag library descriptor, see the appendix entitled Chapter 37, spring-form.tld

•Beans whose lifecycle is scoped to the current HTTP request or HTTP Session. This is not a specific

feature of Spring MVC itself, but rather of the WebApplicationContext container(s) that Spring

MVC uses. These bean scopes are described in the section called “Request, session, and global

session scopes”

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 438

Pluggability of other MVC implementations

Non-Spring MVC implementations are preferable for some projects. Many teams expect to leverage

their existing investment in skills and tools, for example with JSF.

If you do not want to use Spring’s Web MVC, but intend to leverage other solutions that Spring

offers, you can integrate the web MVC framework of your choice with Spring easily. Simply start up

a Spring root application context through its ContextLoaderListener, and access it through its

ServletContext attribute (or Spring’s respective helper method) from within any action object. No

"plug-ins" are involved, so no dedicated integration is necessary. From the web layer’s point of view,

you simply use Spring as a library, with the root application context instance as the entry point.

Your registered beans and Spring’s services can be at your fingertips even without Spring’s Web MVC.

Spring does not compete with other web frameworks in this scenario. It simply addresses the many

areas that the pure web MVC frameworks do not, from bean configuration to data access and transaction

handling. So you can enrich your application with a Spring middle tier and/or data access tier, even if

you just want to use, for example, the transaction abstraction with JDBC or Hibernate.

17.2 The DispatcherServlet

Spring’s web MVC framework is, like many other web MVC frameworks, request-driven, designed

around a central Servlet that dispatches requests to controllers and offers other functionality that

facilitates the development of web applications. Spring’s DispatcherServlet however, does more

than just that. It is completely integrated with the Spring IoC container and as such allows you to use

every other feature that Spring has.

The request processing workflow of the Spring Web MVC DispatcherServlet is illustrated in

the following diagram. The pattern-savvy reader will recognize that the DispatcherServlet is an

expression of the "Front Controller" design pattern (this is a pattern that Spring Web MVC shares with

many other leading web frameworks).

Figure 17.1.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 439

The request processing workflow in Spring Web MVC (high level)

The DispatcherServlet is an actual Servlet (it inherits from the HttpServlet base class), and

as such is declared in the web.xml of your web application. You need to map requests that you want the

DispatcherServlet to handle, by using a URL mapping in the same web.xml file. This is standard

Java EE Servlet configuration; the following example shows such a DispatcherServlet declaration

and mapping:

<web-app>

<servlet-name>example</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>example</servlet-name>

<url-pattern>/example/*</url-pattern>

</servlet-mapping>

</web-app>

In the preceding example, all requests starting with /example will be handled by the

DispatcherServlet instance named example. In a Servlet 3.0+ environment, you also have the

option of configuring the Servlet container programmatically. Below is the code based equivalent of the

above web.xml example:

public class MyWebApplicationInitializer implements WebApplicationInitializer {

@Override

public void onStartup(ServletContext container) {

ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new

DispatcherServlet());

registration.setLoadOnStartup(1);

registration.addMapping("/example/*");

}

WebApplicationInitializer is an interface provided by Spring MVC that ensures your code-based

configuration is detected and automatically used to initialize any Servlet 3 container. An abstract base

class implementation of this interace named AbstractDispatcherServletInitializer makes it

even easier to register the DispatcherServlet by simply specifying its servlet mapping. See Code-

based Servlet container initialization for more details.

The above is only the first step in setting up Spring Web MVC. You now need to configure the various

beans used by the Spring Web MVC framework (over and above the DispatcherServlet itself).

As detailed in Section 5.15, “Additional Capabilities of the ApplicationContext”, ApplicationContext

instances in Spring can be scoped. In the Web MVC framework, each DispatcherServlet

has its own WebApplicationContext, which inherits all the beans already defined in the root

WebApplicationContext. These inherited beans can be overridden in the servlet-specific scope,

and you can define new scope-specific beans local to a given Servlet instance.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 440

Figure 17.2. Context hierarchy in Spring Web MVC

Upon initialization of a DispatcherServlet, Spring MVC looks for a file named [servlet-name]-

servlet.xml in the WEB-INF directory of your web application and creates the beans defined there,

overriding the definitions of any beans defined with the same name in the global scope.

Consider the following DispatcherServlet Servlet configuration (in the web.xml file):

<web-app>

<servlet-name>golfing</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>golfing</servlet-name>

<url-pattern>/golfing/*</url-pattern>

</servlet-mapping>

</web-app>

With the above Servlet configuration in place, you will need to have a file called /WEB-INF/golfing-

servlet.xml in your application; this file will contain all of your Spring Web MVC-specific components

(beans). You can change the exact location of this configuration file through a Servlet initialization

parameter (see below for details).

It is also possible to have just one root context for single DispatcherServlet scenarios by setting an

empty contextConfigLocation servlet init parameter, as shown below:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 441

<web-app>

<context-param>

<param-name>contextConfigLocation</param-name>

<param-value>/WEB-INF/root-context.xml</param-value>

</context-param>

<servlet-name>dispatcher</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

<init-param>

<param-name>contextConfigLocation</param-name>

<param-value></param-value>

</init-param>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>dispatcher</servlet-name>

<url-pattern>/*</url-pattern>

</servlet-mapping>

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

</web-app>

The WebApplicationContext is an extension of the plain ApplicationContext that has some

extra features necessary for web applications. It differs from a normal ApplicationContext in that it

is capable of resolving themes (see Section 17.9, “Using themes”), and that it knows which Servlet it is

associated with (by having a link to the ServletContext). The WebApplicationContext is bound

in the ServletContext, and by using static methods on the RequestContextUtils class you can

always look up the WebApplicationContext if you need access to it.

Special Bean Types In the WebApplicationContext

The Spring DispatcherServlet uses special beans to process requests and render the appropriate

views. These beans are part of Spring MVC. You can choose which special beans to use by simply

configuring one or more of them in the WebApplicationContext. However, you don’t need to do that

initially since Spring MVC maintains a list of default beans to use if you don’t configure any. More on that

in the next section. First see the table below listing the special bean types the DispatcherServlet

relies on.

Table 17.1. Special bean types in the WebApplicationContext

Bean type Explanation

HandlerMapping Maps incoming requests to handlers and a list of

pre- and post-processors (handler interceptors)

based on some criteria the details of which vary

by HandlerMapping implementation. The most

popular implementation supports annotated

controllers but other implementations exists as

well.

HandlerAdapter Helps the DispatcherServlet to invoke

a handler mapped to a request regardless of

the handler is actually invoked. For example,

invoking an annotated controller requires

resolving various annotations. Thus the main

purpose of a HandlerAdapter is to shield the

DispatcherServlet from such details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 442

Bean type Explanation

HandlerExceptionResolver Maps exceptions to views also allowing for more

complex exception handling code.

ViewResolver Resolves logical String-based view names to

actual View types.

LocaleResolver & LocaleContextResolver Resolves the locale a client is using and possibly

their time zone, in order to be able to offer

internationalized views

ThemeResolver Resolves themes your web application can use,

for example, to offer personalized layouts

MultipartResolver Parses multi-part requests for example to

support processing file uploads from HTML

forms.

FlashMapManager Stores and retrieves the "input" and the "output"

FlashMap that can be used to pass attributes

from one request to another, usually across a

redirect.

Default DispatcherServlet Configuration

As mentioned in the previous section for each special bean the DispatcherServlet

maintains a list of implementations to use by default. This information is kept in the file

DispatcherServlet.properties in the package org.springframework.web.servlet.

All special beans have some reasonable defaults of their own. Sooner or later though you’ll need

to customize one or more of the properties these beans provide. For example it’s quite common to

configure an InternalResourceViewResolver settings its prefix property to the parent location

of view files.

Regardless of the details, the important concept to understand here is that once you configure a

special bean such as an InternalResourceViewResolver in your WebApplicationContext,

you effectively override the list of default implementations that would have been used otherwise for that

special bean type. For example if you configure an InternalResourceViewResolver, the default

list of ViewResolver implementations is ignored.

In Section 17.16, “Configuring Spring MVC” you’ll learn about other options for configuring Spring MVC

including MVC Java config and the MVC XML namespace both of which provide a simple starting point

and assume little knowledge of how Spring MVC works. Regardless of how you choose to configure

your application, the concepts explained in this section are fundamental should be of help to you.

DispatcherServlet Processing Sequence

After you set up a DispatcherServlet, and a request comes in for that specific

DispatcherServlet, the DispatcherServlet starts processing the request as follows:

• The WebApplicationContext is searched for and bound in the request as an attribute that

the controller and other elements in the process can use. It is bound by default under the key

DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 443

• The locale resolver is bound to the request to enable elements in the process to resolve the locale

to use when processing the request (rendering the view, preparing data, and so on). If you do not

need locale resolving, you do not need it.

• The theme resolver is bound to the request to let elements such as views determine which theme to

use. If you do not use themes, you can ignore it.

• If you specify a multipart file resolver, the request is inspected for multiparts; if multiparts are found, the

request is wrapped in a MultipartHttpServletRequest for further processing by other elements

in the process. See Section 17.10, “Spring’s multipart (file upload) support” for further information

about multipart handling.

• An appropriate handler is searched for. If a handler is found, the execution chain associated with the

handler (preprocessors, postprocessors, and controllers) is executed in order to prepare a model or

rendering.

• If a model is returned, the view is rendered. If no model is returned, (may be due to a preprocessor or

postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because

the request could already have been fulfilled.

Handler exception resolvers that are declared in the WebApplicationContext pick up exceptions

that are thrown during processing of the request. Using these exception resolvers allows you to define

custom behaviors to address exceptions.

The Spring DispatcherServlet also supports the return of the last-modification-date, as specified

by the Servlet API. The process of determining the last modification date for a specific request

is straightforward: the DispatcherServlet looks up an appropriate handler mapping and tests

whether the handler that is found implements the LastModified interface. If so, the value of the long

getLastModified(request) method of the LastModified interface is returned to the client.

You can customize individual DispatcherServlet instances by adding Servlet initialization

parameters ( init-param elements) to the Servlet declaration in the web.xml file. See the following

table for the list of supported parameters.

Table 17.2. DispatcherServlet initialization parameters

Parameter Explanation

contextClass Class that implements

WebApplicationContext, which instantiates

the context used by this Servlet. By default, the

XmlWebApplicationContext is used.

contextConfigLocation String that is passed to the context instance

(specified by contextClass) to indicate where

context(s) can be found. The string consists

potentially of multiple strings (using a comma

as a delimiter) to support multiple contexts. In

case of multiple context locations with beans

that are defined twice, the latest location takes

precedence.

namespace Namespace of the WebApplicationContext.

Defaults to [servlet-name]-servlet.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 444

17.3 Implementing Controllers

Controllers provide access to the application behavior that you typically define through a service

interface. Controllers interpret user input and transform it into a model that is represented to the user

by the view. Spring implements a controller in a very abstract way, which enables you to create a wide

variety of controllers.

Spring 2.5 introduced an annotation-based programming model for MVC controllers that uses

annotations such as @RequestMapping, @RequestParam, @ModelAttribute, and so on. This

annotation support is available for both Servlet MVC and Portlet MVC. Controllers implemented in this

style do not have to extend specific base classes or implement specific interfaces. Furthermore, they

do not usually have direct dependencies on Servlet or Portlet APIs, although you can easily configure

access to Servlet or Portlet facilities.

Tip

Available in the spring-projects Org on Github, a number of web applications leverage the

annotation support described in this section including MvcShowcase, MvcAjax, MvcBasic,

PetClinic, PetCare, and others.

@Controller

public class HelloWorldController {

@RequestMapping("/helloWorld")

public String helloWorld(Model model) {

model.addAttribute("message", "Hello World!");

return "helloWorld";

}

As you can see, the @Controller and @RequestMapping annotations allow flexible method names

and signatures. In this particular example the method accepts a Model and returns a view name as

a String, but various other method parameters and return values can be used as explained later in

this section. @Controller and @RequestMapping and a number of other annotations form the basis

for the Spring MVC implementation. This section documents these annotations and how they are most

commonly used in a Servlet environment.

Defining a controller with @Controller

The @Controller annotation indicates that a particular class serves the role of a controller. Spring

does not require you to extend any controller base class or reference the Servlet API. However, you

can still reference Servlet-specific features if you need to.

The @Controller annotation acts as a stereotype for the annotated class, indicating its role. The

dispatcher scans such annotated classes for mapped methods and detects @RequestMapping

annotations (see the next section).

You can define annotated controller beans explicitly, using a standard Spring bean definition in the

dispatcher’s context. However, the @Controller stereotype also allows for autodetection, aligned with

Spring general support for detecting component classes in the classpath and auto-registering bean

definitions for them.

To enable autodetection of such annotated controllers, you add component scanning to your

configuration. Use the spring-context schema as shown in the following XML snippet:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 445

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:component-scan base-package="org.springframework.samples.petclinic.web"/>

</beans>

Mapping Requests With @RequestMapping

You use the @RequestMapping annotation to map URLs such as /appointments onto an entire

class or a particular handler method. Typically the class-level annotation maps a specific request

path (or path pattern) onto a form controller, with additional method-level annotations narrowing the

primary mapping for a specific HTTP method request method ("GET", "POST", etc.) or an HTTP request

parameter condition.

The following example from the Petcare sample shows a controller in a Spring MVC application that

uses this annotation:

@Controller

@RequestMapping("/appointments")

public class AppointmentsController {

private final AppointmentBook appointmentBook;

@Autowired

public AppointmentsController(AppointmentBook appointmentBook) {

this.appointmentBook = appointmentBook;

}

@RequestMapping(method = RequestMethod.GET)

public Map<String, Appointment> get() {

return appointmentBook.getAppointmentsForToday();

}

@RequestMapping(value="/{day}", method = RequestMethod.GET)

public Map<String, Appointment> getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day,

Model model) {

return appointmentBook.getAppointmentsForDay(day);

}

@RequestMapping(value="/new", method = RequestMethod.GET)

public AppointmentForm getNewForm() {

return new AppointmentForm();

}

@RequestMapping(method = RequestMethod.POST)

public String add(@Valid AppointmentForm appointment, BindingResult result) {

if (result.hasErrors()) {

return "appointments/new";

}

appointmentBook.addAppointment(appointment);

return "redirect:/appointments";

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 446

In the example, the @RequestMapping is used in a number of places. The first usage is on the

type (class) level, which indicates that all handling methods on this controller are relative to the /

appointments path. The get() method has a further @RequestMapping refinement: it only accepts

GET requests, meaning that an HTTP GET for /appointments invokes this method. The post() has

a similar refinement, and the getNewForm() combines the definition of HTTP method and path into

one, so that GET requests for appointments/new are handled by that method.

The getForDay() method shows another usage of @RequestMapping: URI templates. (See the next

section).

A @RequestMapping on the class level is not required. Without it, all paths are simply absolute, and

not relative. The following example from the PetClinic sample application shows a multi-action controller

using @RequestMapping:

@Controller

public class ClinicController {

private final Clinic clinic;

@Autowired

public ClinicController(Clinic clinic) {

this.clinic = clinic;

}

@RequestMapping("/")

public void welcomeHandler() {

}

@RequestMapping("/vets")

public ModelMap vetsHandler() {

return new ModelMap(this.clinic.getVets());

}

@Controller's and AOP Proxying

In some cases a controller may need to be decorated with an AOP proxy at runtime. One example is if

you choose to have @Transactional annotations directly on the controller. When this is the case, for

controllers specifically, we recommend using class-based proxying. This is typically the default choice

with controllers. However if a controller must implement an interface that is not a Spring Context callback

(e.g. InitializingBean, *Aware, etc), you may need to explicitly configure class-based proxying.

For example with <tx:annotation-driven />, change to <tx:annotation-driven proxy-

target-class="true" />.

New Support Classes for @RequestMapping methods in Spring MVC 3.1

Spring 3.1 introduced a new set of support classes for @RequestMapping methods called

RequestMappingHandlerMapping and RequestMappingHandlerAdapter respectively. They

are recommended for use and even required to take advantage of new features in Spring MVC 3.1 and

going forward. The new support classes are enabled by default by the MVC namespace and the MVC

Java config but must be configured explicitly if using neither. This section describes a few important

differences between the old and the new support classes.

Prior to Spring 3.1, type and method-level request mappings were examined in two separate stages — a

controller was selected first by the DefaultAnnotationHandlerMapping and the actual method to

invoke was narrowed down second by the AnnotationMethodHandlerAdapter.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 447

With the new support classes in Spring 3.1, the RequestMappingHandlerMapping is the only place

where a decision is made about which method should process the request. Think of controller methods

as a collection of unique endpoints with mappings for each method derived from type and method-level

@RequestMapping information.

This enables some new possibilities. For once a HandlerInterceptor or a

HandlerExceptionResolver can now expect the Object-based handler to be a HandlerMethod,

which allows them to examine the exact method, its parameters and associated annotations. The

processing for a URL no longer needs to be split across different controllers.

There are also several things no longer possible:

• Select a controller first with a SimpleUrlHandlerMapping or BeanNameUrlHandlerMapping

and then narrow the method based on @RequestMapping annotations.

• Rely on method names as a fall-back mechanism to disambiguate between two @RequestMapping

methods that don’t have an explicit path mapping URL path but otherwise match equally, e.g. by HTTP

method. In the new support classes @RequestMapping methods have to be mapped uniquely.

• Have a single default method (without an explicit path mapping) with which requests are processed if

no other controller method matches more concretely. In the new support classes if a matching method

is not found a 404 error is raised.

The above features are still supported with the existing support classes. However to take advantage of

new Spring MVC 3.1 features you’ll need to use the new support classes.

URI Template Patterns

URI templates can be used for convenient access to selected parts of a URL in a @RequestMapping

method.

A URI Template is a URI-like string, containing one or more variable names. When you substitute

values for these variables, the template becomes a URI. The proposed RFC for URI Templates defines

how a URI is parameterized. For example, the URI Template http://www.example.com/users/

{userId} contains the variable userId. Assigning the value fred to the variable yields http://

www.example.com/users/fred.

In Spring MVC you can use the @PathVariable annotation on a method argument to bind it to the

value of a URI template variable:

@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)

public String findOwner(@PathVariable String ownerId, Model model) {

Owner owner = ownerService.findOwner(ownerId);

model.addAttribute("owner", owner);

return "displayOwner";

}

The URI Template " /owners/{ownerId}" specifies the variable name ownerId. When the controller

handles this request, the value of ownerId is set to the value found in the appropriate part of the URI.

For example, when a request comes in for /owners/fred, the value of ownerId is fred.

Tip

To process the @PathVariable annotation, Spring MVC needs to find the matching URI template

variable by name. You can specify it in the annotation:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 448

@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)

public String findOwner(@PathVariable("ownerId") String theOwner, Model model) {

// implementation omitted

}

Or if the URI template variable name matches the method argument name you can omit that detail.

As long as your code is not compiled without debugging information, Spring MVC will match the

method argument name to the URI template variable name:

@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)

public String findOwner(@PathVariable String ownerId, Model model) {

// implementation omitted

}

A method can have any number of @PathVariable annotations:

@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET)

public String findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {

Owner owner = ownerService.findOwner(ownerId);

Pet pet = owner.getPet(petId);

model.addAttribute("pet", pet);

return "displayPet";

}

When a @PathVariable annotation is used on a Map<String, String> argument, the map is

populated with all URI template variables.

A URI template can be assembled from type and path level @RequestMapping annotations. As a result

the findPet() method can be invoked with a URL such as /owners/42/pets/21.

@Controller

@RequestMapping("/owners/{ownerId}")

public class RelativePathUriTemplateController {

@RequestMapping("/pets/{petId}")

public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {

// implementation omitted

}

A @PathVariable argument can be of any simple type such as int, long, Date, etc. Spring automatically

converts to the appropriate type or throws a TypeMismatchException if it fails to do so. You can also

Conversion” and the section called “Customizing WebDataBinder initialization”.

URI Template Patterns with Regular Expressions

Sometimes you need more precision in defining URI template variables. Consider the URL "/spring-

web/spring-web-3.0.5.jar". How do you break it down into multiple parts?

The @RequestMapping annotation supports the use of regular expressions in URI template variables.

The syntax is {varName:regex} where the first part defines the variable name and the second - the

regular expression.For example:

@RequestMapping("/spring-web/{symbolicName:[a-z-]}-{version:\\d\\.\\d\\.\\d}{extension:\\.[a-z]}")

public void handle(@PathVariable String version, @PathVariable String extension) {

// ...

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 449

Path Patterns

In addition to URI templates, the @RequestMapping annotation also supports Ant-style path patterns

(for example, /myPath/*.do). A combination of URI template variables and Ant-style globs is also

supported (e.g. /owners/*/pets/{petId}).

Path Pattern Comparison

When a URL matches multiple patterns, a sort is used to find the most specific match.

A pattern with a lower count of URI variables and wild cards is considered more specific. For example

/hotels/{hotel}/* has 1 URI variable and 1 wild card and is considered more specific than /

hotels/{hotel}/** which as 1 URI variable and 2 wild cards.

If two patterns have the same count, the one that is longer is considered more specific. For example /

foo/bar* is longer and considered more specific than /foo/*.

When two patterns have the same count and length, the pattern with fewer wild cards is considered

more specific. For example /hotels/{hotel} is more specific than /hotels/*.

There are also some additional special rules:

• The default mapping pattern /** is less specific than any other pattern. For example /api/{a}/

{b}/{c} is more specific.

• A prefix pattern such as /public/** is less specific than any other pattern that doesn’t contain

double wildcards. For example /public/path3/{a}/{b}/{c} is more specific.

For the full details see AntPatternComparator in AntPathMatcher. Note that the PathMatcher can

be customized (see the section called “Path Matching” in the section on configuring Spring MVC).

Path Patterns with Placeholders

Patterns in @RequestMapping annotations support ${…} placeholders against local properties and/or

system properties and environment variables. This may be useful in cases where the path a controller

is mapped to may need to be customized through configuration. For more information on placeholders,

see the javadocs of the PropertyPlaceholderConfigurer class.

Path Pattern Matching By Suffix

By default Spring MVC automatically performs ".*" suffix pattern matching so that a controller mapped

to /person is also implicitly mapped to /person.*. This allows indicating content types via file

extensions, e.g. /person.pdf, /person.xml, etc. A common pitfall however is when the last path

segment of the mapping is a URI variable, e.g. /person/{id}. While a request for /person/1.json

would correctly result in path variable id=1 and extension ".json", when the id naturally contains a dot,

e.g. /person/joe@email.com the result does not match expectations. Clearly here ".com" is not a

file extension.

The proper way to address this is to configure Spring MVC to only do suffix pattern matching against

file extensions registered for content negotiation purposes. For more on this, first see the section called

“Content Negotiation” and then the section called “Path Matching” showing how to enable suffix pattern

matching along with how to use registered suffix patterns only.

Matrix Variables

The URI specification RFC 3986 defines the possibility of including name-value pairs within path

segments. There is no specific term used in the spec. The general "URI path parameters" could be

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 450

applied although the more unique "Matrix URIs", originating from an old post by Tim Berners-Lee, is

also frequently used and fairly well known. Within Spring MVC these are referred to as matrix variables.

Matrix variables can appear in any path segment, each matrix variable separated with a

";" (semicolon). For example: "/cars;color=red;year=2012". Multiple values may be either

"," (comma) separated "color=red,green,blue" or the variable name may be repeated

"color=red;color=green;color=blue".

If a URL is expected to contain matrix variables, the request mapping pattern must represent them with a

URI template. This ensures the request can be matched correctly regardless of whether matrix variables

are present or not and in what order they are provided.

Below is an example of extracting the matrix variable "q":

// GET /pets/42;q=11;r=22

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)

public void findPet(@PathVariable String petId, @MatrixVariable int q) {

// petId == 42

// q == 11

}

Since all path segments may contain matrix variables, in some cases you need to be more specific to

identify where the variable is expected to be:

// GET /owners/42;q=11/pets/21;q=22

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)

public void findPet(

@MatrixVariable(value="q", pathVar="ownerId") int q1,

@MatrixVariable(value="q", pathVar="petId") int q2) {

// q1 == 11

// q2 == 22

}

A matrix variable may be defined as optional and a default value specified:

// GET /pets/42

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)

public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) {

// q == 1

}

All matrix variables may be obtained in a Map:

// GET /owners/42;q=11;r=12/pets/21;q=22;s=23

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)

public void findPet(

@MatrixVariable Map<String, String> matrixVars,

@MatrixVariable(pathVar="petId"") Map<String, String> petMatrixVars) {

// matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]

// petMatrixVars: ["q" : 11, "s" : 23]

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 451

Note that to enable the use of matrix variables, you must set the removeSemicolonContent property

of RequestMappingHandlerMapping to false. By default it is set to true.

Tip

The MVC Java config and the MVC namespace both provide options for enabling the use of matrix

variables.

If you are using Java config, The Advanced Customizations with MVC Java Config section

describes how the RequestMappingHandlerMapping can be customized.

In the MVC namespace, the <mvc:annotation-driven> element has an enable-matrix-

variables attribute that should be set to true. By default it is set to false.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven enable-matrix-variables="true"/>

</beans>

Consumable Media Types

You can narrow the primary mapping by specifying a list of consumable media types. The request will

be matched only if the Content-Type request header matches the specified media type. For example:

@Controller

@RequestMapping(value = "/pets", method = RequestMethod.POST, consumes="application/json")

public void addPet(@RequestBody Pet pet, Model model) {

// implementation omitted

}

Consumable media type expressions can also be negated as in !text/plain to match to all requests other

than those with Content-Type of text/plain.

Tip

The consumes condition is supported on the type and on the method level. Unlike most other

conditions, when used at the type level, method-level consumable types override rather than

extend type-level consumable types.

Producible Media Types

You can narrow the primary mapping by specifying a list of producible media types. The request will

be matched only if the Accept request header matches one of these values. Furthermore, use of the

produces condition ensures the actual content type used to generate the response respects the media

types specified in the produces condition. For example:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 452

@Controller

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json")

@ResponseBody

public Pet getPet(@PathVariable String petId, Model model) {

// implementation omitted

}

Just like with consumes, producible media type expressions can be negated as in !text/plain to match

to all requests other than those with an Accept header value of text/plain.

Tip

The produces condition is supported on the type and on the method level. Unlike most other

conditions, when used at the type level, method-level producible types override rather than extend

type-level producible types.

Request Parameters and Header Values

You can narrow request matching through request parameter conditions such as "myParam", "!

myParam", or "myParam=myValue". The first two test for request parameter presence/absence and

the third for a specific parameter value. Here is an example with a request parameter value condition:

@Controller

@RequestMapping("/owners/{ownerId}")

public class RelativePathUriTemplateController {

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue")

public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {

// implementation omitted

}

The same can be done to test for request header presence/absence or to match based on a specific

request header value:

@Controller

@RequestMapping("/owners/{ownerId}")

public class RelativePathUriTemplateController {

@RequestMapping(value = "/pets", method = RequestMethod.GET, headers="myHeader=myValue")

public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {

// implementation omitted

}

Tip

Although you can match to Content-Type and Accept header values using media type wild cards

(for example "content-type=text/*" will match to "text/plain" and "text/html"), it is recommended to

use the consumes and produces conditions respectively instead. They are intended specifically

for that purpose.

Defining @RequestMapping handler methods

An @RequestMapping handler method can have a very flexible signatures. The supported method

arguments and return values are described in the following section. Most arguments can be used in

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 453

arbitrary order with the only exception of BindingResult arguments. This is described in the next

section.

Note

Spring 3.1 introduced a new set of support classes for @RequestMapping methods called

RequestMappingHandlerMapping and RequestMappingHandlerAdapter respectively.

They are recommended for use and even required to take advantage of new features in Spring

MVC 3.1 and going forward. The new support classes are enabled by default from the MVC

namespace and with use of the MVC Java config but must be configured explicitly if using neither.

Supported method argument types

The following are the supported method arguments:

• Request or response objects (Servlet API). Choose any specific request or response type, for example

ServletRequest or HttpServletRequest.

• Session object (Servlet API): of type HttpSession. An argument of this type enforces the presence

of a corresponding session. As a consequence, such an argument is never null.

Note

Session access may not be thread-safe, in particular in a Servlet environment. Consider setting the

RequestMappingHandlerAdapter's "synchronizeOnSession" flag to "true" if multiple requests

are allowed to access a session concurrently.

•org.springframework.web.context.request.WebRequest or

org.springframework.web.context.request.NativeWebRequest. Allows for generic

request parameter access as well as request/session attribute access, without ties to the native

Servlet/Portlet API.

•java.util.Locale for the current request locale, determined by the most specific locale resolver

available, in effect, the configured LocaleResolver in a Servlet environment.

•java.io.InputStream / java.io.Reader for access to the request’s content. This value is the

raw InputStream/Reader as exposed by the Servlet API.

•java.io.OutputStream / java.io.Writer for generating the response’s content. This value is

the raw OutputStream/Writer as exposed by the Servlet API.

•org.springframework.http.HttpMethod for the HTTP request method.

•java.security.Principal containing the currently authenticated user.

•@PathVariable annotated parameters for access to URI template variables. See the section called

“URI Template Patterns”.

•@MatrixVariable annotated parameters for access to name-value pairs located in URI path

segments. See the section called “Matrix Variables”.

•@RequestParam annotated parameters for access to specific Servlet request parameters. Parameter

values are converted to the declared method argument type. See the section called “Binding request

parameters to method parameters with @RequestParam”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 454

•@RequestHeader annotated parameters for access to specific Servlet request HTTP headers.

Parameter values are converted to the declared method argument type.

•@RequestBody annotated parameters for access to the HTTP request body. Parameter values are

converted to the declared method argument type using HttpMessageConverters. See the section

called “Mapping the request body with the @RequestBody annotation”.

•@RequestPart annotated parameters for access to the content of a "multipart/form-data" request

part. See the section called “Handling a file upload request from programmatic clients” and

Section 17.10, “Spring’s multipart (file upload) support”.

•HttpEntity<?> parameters for access to the Servlet request HTTP headers and contents. The

request stream will be converted to the entity body using HttpMessageConverters. See the section

called “Using HttpEntity”.

•java.util.Map / org.springframework.ui.Model /

org.springframework.ui.ModelMap for enriching the implicit model that is exposed to the web

view.

•org.springframework.web.servlet.mvc.support.RedirectAttributes to specify the

exact set of attributes to use in case of a redirect and also to add flash attributes (attributes

stored temporarily on the server-side to make them available to the request after the redirect).

RedirectAttributes is used instead of the implicit model if the method returns a "redirect:"

prefixed view name or RedirectView.

• Command or form objects to bind request parameters to bean properties (via setters) or

directly to fields, with customizable type conversion, depending on @InitBinder methods

and/or the HandlerAdapter configuration. See the webBindingInitializer property on

RequestMappingHandlerAdapter. Such command objects along with their validation results will

be exposed as model attributes by default, using the command class class name - e.g. model attribute

"orderAddress" for a command object of type "some.package.OrderAddress". The ModelAttribute

annotation can be used on a method argument to customize the model attribute name used.

•org.springframework.validation.Errors /

org.springframework.validation.BindingResult validation results for a preceding

command or form object (the immediately preceding method argument).

•org.springframework.web.bind.support.SessionStatus status handle for marking form

processing as complete, which triggers the cleanup of session attributes that have been indicated by

the @SessionAttributes annotation at the handler type level.

•org.springframework.web.util.UriComponentsBuilder a builder for preparing a URL

relative to the current request’s host, port, scheme, context path, and the literal part of the servlet

mapping.

The Errors or BindingResult parameters have to follow the model object that is being bound

immediately as the method signature might have more that one model object and Spring will create a

separate BindingResult instance for each of them so the following sample won’t work:

Invalid ordering of BindingResult and @ModelAttribute.

@RequestMapping(method = RequestMethod.POST)

public String processSubmit(@ModelAttribute("pet") Pet pet, Model model, BindingResult result) { ... }

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 455

Note, that there is a Model parameter in between Pet and BindingResult. To get this working you

have to reorder the parameters as follows:

@RequestMapping(method = RequestMethod.POST)

public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result, Model model) { ... }

Supported method return types

The following are the supported return types:

• A ModelAndView object, with the model implicitly enriched with command objects and the results of

@ModelAttribute annotated reference data accessor methods.

• A Model object, with the view name implicitly determined through a

RequestToViewNameTranslator and the model implicitly enriched with command objects and the

results of @ModelAttribute annotated reference data accessor methods.

• A Map object for exposing a model, with the view name implicitly determined through a

RequestToViewNameTranslator and the model implicitly enriched with command objects and the

results of @ModelAttribute annotated reference data accessor methods.

• A View object, with the model implicitly determined through command objects and

@ModelAttribute annotated reference data accessor methods. The handler method may also

programmatically enrich the model by declaring a Model argument (see above).

• A String value that is interpreted as the logical view name, with the model implicitly determined

through command objects and @ModelAttribute annotated reference data accessor methods. The

handler method may also programmatically enrich the model by declaring a Model argument (see

above).

•void if the method handles the response itself (by writing the response content directly, declaring

an argument of type ServletResponse / HttpServletResponse for that purpose) or if the view

name is supposed to be implicitly determined through a RequestToViewNameTranslator (not

declaring a response argument in the handler method signature).

• If the method is annotated with @ResponseBody, the return type is written to the response

HTTP body. The return value will be converted to the declared method argument type using

HttpMessageConverters. See the section called “Mapping the response body with the

@ResponseBody annotation”.

• An HttpEntity<?> or ResponseEntity<?> object to provide access to the Servlet response

HTTP headers and contents. The entity body will be converted to the response stream using

HttpMessageConverters. See the section called “Using HttpEntity”.

• An HttpHeaders object to return a response with no body.

• A Callable<?> can be returned when the application wants to produce the return value

asynchronously in a thread managed by Spring MVC.

• A DeferredResult<?> can be returned when the application wants to produce the return value

from a thread of its own choosing.

• A ListenableFuture<?> can be returned when the application wants to produce the return value

from a thread of its own choosing.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 456

• Any other return type is considered to be a single model attribute to be exposed to the view, using

the attribute name specified through @ModelAttribute at the method level (or the default attribute

name based on the return type class name). The model is implicitly enriched with command objects

and the results of @ModelAttribute annotated reference data accessor methods.

Binding request parameters to method parameters with @RequestParam

Use the @RequestParam annotation to bind request parameters to a method parameter in your

controller.

The following code snippet shows the usage:

@Controller

@RequestMapping("/pets")

@SessionAttributes("pet")

public class EditPetForm {

// ...

@RequestMapping(method = RequestMethod.GET)

public String setupForm(@RequestParam("petId") int petId, ModelMap model) {

Pet pet = this.clinic.loadPet(petId);

model.addAttribute("pet", pet);

return "petForm";

}

// ...

}

Parameters using this annotation are required by default, but you can specify that a parameter is optional

by setting @RequestParam's required attribute to false (e.g., @RequestParam(value="id",

required=false)).

Type conversion is applied automatically if the target method parameter type is not String. See the

section called “Method Parameters And Type Conversion”.

Mapping the request body with the @RequestBody annotation

The @RequestBody method parameter annotation indicates that a method parameter should be bound

to the value of the HTTP request body. For example:

@RequestMapping(value = "/something", method = RequestMethod.PUT)

public void handle(@RequestBody String body, Writer writer) throws IOException {

writer.write(body);

}

You convert the request body to the method argument by using an HttpMessageConverter.

HttpMessageConverter is responsible for converting from the HTTP request message to an object

and converting from an object to the HTTP response body. The RequestMappingHandlerAdapter

supports the @RequestBody annotation with the following default HttpMessageConverters:

•ByteArrayHttpMessageConverter converts byte arrays.

•StringHttpMessageConverter converts strings.

•FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>.

•SourceHttpMessageConverter converts to/from a javax.xml.transform.Source.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 457

For more information on these converters, see Message Converters. Also note that if using the MVC

namespace or the MVC Java config, a wider range of message converters are registered by default. See

the section called “Enabling the MVC Java Config or the MVC XML Namespace” for more information.

If you intend to read and write XML, you will need to configure the

MarshallingHttpMessageConverter with a specific Marshaller and an Unmarshaller

implementation from the org.springframework.oxm package. The example below shows how to do

that directly in your configuration but if your application is configured through the MVC namespace or the

MVC Java config see the section called “Enabling the MVC Java Config or the MVC XML Namespace”

instead.

<util:list id="beanList">

</util:list>

</property

</bean>

<bean id="stringHttpMessageConverter"

class="org.springframework.http.converter.StringHttpMessageConverter"/>

<bean id="marshallingHttpMessageConverter"

class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">

</bean>

An @RequestBody method parameter can be annotated with @Valid, in which case it will be validated

using the configured Validator instance. When using the MVC namespace or the MVC Java config,

a JSR-303 validator is configured automatically assuming a JSR-303 implementation is available on

the classpath.

Just like with @ModelAttribute parameters, an Errors argument can be used to examine the errors.

If such an argument is not declared, a MethodArgumentNotValidException will be raised. The

exception is handled in the DefaultHandlerExceptionResolver, which sends a 400 error back

to the client.

Note

Also see the section called “Enabling the MVC Java Config or the MVC XML Namespace” for

information on configuring message converters and a validator through the MVC namespace or

the MVC Java config.

Mapping the response body with the @ResponseBody annotation

The @ResponseBody annotation is similar to @RequestBody. This annotation can be put on a method

and indicates that the return type should be written straight to the HTTP response body (and not placed

in a Model, or interpreted as a view name). For example:

@RequestMapping(value = "/something", method = RequestMethod.PUT)

@ResponseBody

public String helloWorld() {

return "Hello World";

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 458

The above example will result in the text Hello World being written to the HTTP response stream.

As with @RequestBody, Spring converts the returned object to a response body by using an

HttpMessageConverter. For more information on these converters, see the previous section and

Message Converters.

Creating REST Controllers with the @RestController annotation

It’s a very common use case to have Controllers implement a REST API, thus serving only JSON, XML

or custom MediaType content. For convenience, instead of annotating all your @RequestMapping

methods with @ResponseBody, you can annotate your Controller Class with @RestController.

@RestController is a stereotype annotation that combines @ResponseBody and @Controller.

More than that, it gives more meaning to your Controller and also may carry additional semantics in

future releases of the framework.

As with regular @Controllers, a @RestController may be assisted by a @ControllerAdvice

Bean. See the the section called “Advising controllers with the @ControllerAdvice annotation”

section for more details.

Using HttpEntity

The HttpEntity is similar to @RequestBody and @ResponseBody. Besides getting access to the

request and response body, HttpEntity (and the response-specific subclass ResponseEntity) also

allows access to the request and response headers, like so:

@RequestMapping("/something")

public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws

UnsupportedEncodingException {

String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader"));

byte[] requestBody = requestEntity.getBody();

// do something with request header and body

HttpHeaders responseHeaders = new HttpHeaders();

responseHeaders.set("MyResponseHeader", "MyValue");

return new ResponseEntity<String>("Hello World", responseHeaders, HttpStatus.CREATED);

}

The above example gets the value of the MyRequestHeader request header, and reads the body as

a byte array. It adds the MyResponseHeader to the response, writes Hello World to the response

stream, and sets the response status code to 201 (Created).

As with @RequestBody and @ResponseBody, Spring uses HttpMessageConverter to convert from

and to the request and response streams. For more information on these converters, see the previous

section and Message Converters.

Using @ModelAttribute on a method

The @ModelAttribute annotation can be used on methods or on method arguments. This section

explains its usage on methods while the next section explains its usage on method arguments.

An @ModelAttribute on a method indicates the purpose of that method is to add one or more model

attributes. Such methods support the same argument types as @RequestMapping methods but cannot

be mapped directly to requests. Instead @ModelAttribute methods in a controller are invoked before

@RequestMapping methods, within the same controller. A couple of examples:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 459

// Add one attribute

// The return value of the method is added to the model under the name "account"

// You can customize the name via @ModelAttribute("myAccount")

@ModelAttribute

public Account addAccount(@RequestParam String number) {

return accountManager.findAccount(number);

}

// Add multiple attributes

@ModelAttribute

public void populateModel(@RequestParam String number, Model model) {

model.addAttribute(accountManager.findAccount(number));

// add more ...

}

@ModelAttribute methods are used to populate the model with commonly needed attributes for

example to fill a drop-down with states or with pet types, or to retrieve a command object like Account

in order to use it to represent the data on an HTML form. The latter case is further discussed in the

next section.

Note the two styles of @ModelAttribute methods. In the first, the method adds an attribute implicitly

by returning it. In the second, the method accepts a Model and adds any number of model attributes

to it. You can choose between the two styles depending on your needs.

A controller can have any number of @ModelAttribute methods. All such methods are invoked before

@RequestMapping methods of the same controller.

@ModelAttribute methods can also be defined in an @ControllerAdvice-annotated class and

such methods apply to many controllers. See the the section called “Advising controllers with the

@ControllerAdvice annotation” section for more details.

Tip

What happens when a model attribute name is not explicitly specified? In such cases a default

name is assigned to the model attribute based on its type. For example if the method returns an

object of type Account, the default name used is "account". You can change that through the

value of the @ModelAttribute annotation. If adding attributes directly to the Model, use the

appropriate overloaded addAttribute(..) method - i.e., with or without an attribute name.

The @ModelAttribute annotation can be used on @RequestMapping methods as well. In that case

the return value of the @RequestMapping method is interpreted as a model attribute rather than as

a view name. The view name is derived from view name conventions instead much like for methods

returning void — see the section called “The View - RequestToViewNameTranslator”.

Using @ModelAttribute on a method argument

As explained in the previous section @ModelAttribute can be used on methods or on method

arguments. This section explains its usage on method arguments.

An @ModelAttribute on a method argument indicates the argument should be retrieved from the

model. If not present in the model, the argument should be instantiated first and then added to the model.

Once present in the model, the argument’s fields should be populated from all request parameters that

have matching names. This is known as data binding in Spring MVC, a very useful mechanism that

saves you from having to parse each form field individually.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 460

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)

public String processSubmit(@ModelAttribute Pet pet) { }

Given the above example where can the Pet instance come from? There are several options:

• It may already be in the model due to use of @SessionAttributes — see the section called “Using

@SessionAttributes to store model attributes in the HTTP session between requests”.

• It may already be in the model due to an @ModelAttribute method in the same controller — as

explained in the previous section.

• It may be retrieved based on a URI template variable and type converter (explained in more detail

below).

• It may be instantiated using its default constructor.

An @ModelAttribute method is a common way to to retrieve an attribute from the database, which

may optionally be stored between requests through the use of @SessionAttributes. In some cases

it may be convenient to retrieve the attribute by using an URI template variable and a type converter.

Here is an example:

@RequestMapping(value="/accounts/{account}", method = RequestMethod.PUT)

public String save(@ModelAttribute("account") Account account) {

}

In this example the name of the model attribute (i.e. "account") matches the name of a URI template

variable. If you register Converter<String, Account> that can turn the String account value into

an Account instance, then the above example will work without the need for an @ModelAttribute

method.

The next step is data binding. The WebDataBinder class matches request parameter

names — including query string parameters and form fields — to model attribute fields by name.

Matching fields are populated after type conversion (from String to the target field type) has been applied

where necessary. Data binding and validation are covered in Chapter 7, Validation, Data Binding, and

Type Conversion. Customizing the data binding process for a controller level is covered in the section

called “Customizing WebDataBinder initialization”.

As a result of data binding there may be errors such as missing required fields or type conversion

errors. To check for such errors add a BindingResult argument immediately following the

@ModelAttribute argument:

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)

public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {

if (result.hasErrors()) {

return "petForm";

}

// ...

}

With a BindingResult you can check if errors were found in which case it’s common to render the

same form where the errors can be shown with the help of Spring’s <errors> form tag.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 461

In addition to data binding you can also invoke validation using your own custom validator passing the

same BindingResult that was used to record data binding errors. That allows for data binding and

validation errors to be accumulated in one place and subsequently reported back to the user:

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)

public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {

new PetValidator().validate(pet, result);

if (result.hasErrors()) {

return "petForm";

}

// ...

}

Or you can have validation invoked automatically by adding the JSR-303 @Valid annotation:

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)

public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) {

if (result.hasErrors()) {

return "petForm";

}

// ...

}

See Section 7.8, “Spring Validation” and Chapter 7, Validation, Data Binding, and Type Conversion for

details on how to configure and use validation.

Using @SessionAttributes to store model attributes in the HTTP session between requests

The type-level @SessionAttributes annotation declares session attributes used by a specific

handler. This will typically list the names of model attributes or types of model attributes which should

be transparently stored in the session or some conversational storage, serving as form-backing beans

between subsequent requests.

The following code snippet shows the usage of this annotation, specifying the model attribute name:

@Controller

@RequestMapping("/editPet.do")

@SessionAttributes("pet")

public class EditPetForm {

// ...

}

Specifying redirect and flash attributes

By default all model attributes are considered to be exposed as URI template variables in the redirect

URL. Of the remaining attributes those that are primitive types or collections/arrays of primitive types

are automatically appended as query parameters.

In annotated controllers however the model may contain additional attributes originally added

for rendering purposes (e.g. drop-down field values). To gain precise control over the attributes

used in a redirect scenario, an @RequestMapping method can declare an argument of type

RedirectAttributes and use it to add attributes for use in RedirectView. If the controller method

does redirect, the content of RedirectAttributes is used. Otherwise the content of the default

Model is used.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 462

The RequestMappingHandlerAdapter provides a flag called

"ignoreDefaultModelOnRedirect" that can be used to indicate the content of the default Model

should never be used if a controller method redirects. Instead the controller method should declare

an attribute of type RedirectAttributes or if it doesn’t do so no attributes should be passed on

to RedirectView. Both the MVC namespace and the MVC Java config keep this flag set to false

in order to maintain backwards compatibility. However, for new applications we recommend setting it

to true

The RedirectAttributes interface can also be used to add flash attributes. Unlike other redirect

attributes, which end up in the target redirect URL, flash attributes are saved in the HTTP session

(and hence do not appear in the URL). The model of the controller serving the target redirect URL

automatically receives these flash attributes after which they are removed from the session. See

Section 17.6, “Using flash attributes” for an overview of the general support for flash attributes in Spring

MVC.

Working with "application/x-www-form-urlencoded" data

The previous sections covered use of @ModelAttribute to support form submission requests

from browser clients. The same annotation is recommended for use with requests from non-browser

clients as well. However there is one notable difference when it comes to working with HTTP PUT

requests. Browsers can submit form data via HTTP GET or HTTP POST. Non-browser clients can also

submit forms via HTTP PUT. This presents a challenge because the Servlet specification requires the

ServletRequest.getParameter*() family of methods to support form field access only for HTTP

POST, not for HTTP PUT.

To support HTTP PUT and PATCH requests, the spring-web module provides the filter

HttpPutFormContentFilter, which can be configured in web.xml:

<filter-name>httpPutFormFilter</filter-name>

<filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>httpPutFormFilter</filter-name>

<servlet-name>dispatcherServlet</servlet-name>

</filter-mapping>

<servlet-name>dispatcherServlet</servlet-name>

<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

</servlet>

The above filter intercepts HTTP PUT and PATCH requests with content type application/

x-www-form-urlencoded, reads the form data from the body of the request, and

wraps the ServletRequest in order to make the form data available through the

ServletRequest.getParameter*() family of methods.

Note

As HttpPutFormContentFilter consumes the body of the request, it should not be configured

for PUT or PATCH URLs that rely on other converters for application/x-www-form-

urlencoded. This includes @RequestBody MultiValueMap<String, String> and

HttpEntity<MultiValueMap<String, String>>.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 463

Mapping cookie values with the @CookieValue annotation

The @CookieValue annotation allows a method parameter to be bound to the value of an HTTP cookie.

Let us consider that the following cookie has been received with an http request:

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

The following code sample demonstrates how to get the value of the JSESSIONID cookie:

@RequestMapping("/displayHeaderInfo.do")

public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {

//...

}

Type conversion is applied automatically if the target method parameter type is not String. See the

section called “Method Parameters And Type Conversion”.

This annotation is supported for annotated handler methods in Servlet and Portlet environments.

Mapping request header attributes with the @RequestHeader annotation

The @RequestHeader annotation allows a method parameter to be bound to a request header.

Here is a sample request header:

Host localhost:8080

Accept text/html,application/xhtml+xml,application/xml;q=0.9

Accept-Language fr,en-gb;q=0.7,en;q=0.3

Accept-Encoding gzip,deflate

Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7

Keep-Alive 300

The following code sample demonstrates how to get the value of the Accept-Encoding and Keep-

Alive headers:

@RequestMapping("/displayHeaderInfo.do")

public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,

@RequestHeader("Keep-Alive") long keepAlive) {

//...

}

Type conversion is applied automatically if the method parameter is not String. See the section called

“Method Parameters And Type Conversion”.

Tip

Built-in support is available for converting a comma-separated string into an array/collection of

strings or other types known to the type conversion system. For example a method parameter

annotated with @RequestHeader("Accept") may be of type String but also String[] or

List<String>.

This annotation is supported for annotated handler methods in Servlet and Portlet environments.

Method Parameters And Type Conversion

String-based values extracted from the request including request parameters, path variables, request

headers, and cookie values may need to be converted to the target type of the method parameter or

field (e.g., binding a request parameter to a field in an @ModelAttribute parameter) they’re bound

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 464

to. If the target type is not String, Spring automatically converts to the appropriate type. All simple

types such as int, long, Date, etc. are supported. You can further customize the conversion process

through a WebDataBinder (see the section called “Customizing WebDataBinder initialization”) or by

registering Formatters with the FormattingConversionService (see Section 7.6, “Spring Field

Formatting”).

Customizing WebDataBinder initialization

To customize request parameter binding with PropertyEditors through Spring’s WebDataBinder, you

can use @InitBinder-annotated methods within your controller, @InitBinder methods within an

@ControllerAdvice class, or provide a custom WebBindingInitializer. See the the section

called “Advising controllers with the @ControllerAdvice annotation” section for more details.

Customizing data binding with @InitBinder

Annotating controller methods with @InitBinder allows you to configure web data binding directly

within your controller class. @InitBinder identifies methods that initialize the WebDataBinder that

will be used to populate command and form object arguments of annotated handler methods.

Such init-binder methods support all arguments that @RequestMapping supports, except for

command/form objects and corresponding validation result objects. Init-binder methods must not have

a return value. Thus, they are usually declared as void. Typical arguments include WebDataBinder

in combination with WebRequest or java.util.Locale, allowing code to register context-specific

editors.

The following example demonstrates the use of @InitBinder to configure a CustomDateEditor for

all java.util.Date form properties.

@Controller

public class MyFormController {

@InitBinder

public void initBinder(WebDataBinder binder) {

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");

dateFormat.setLenient(false);

binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));

}

// ...

}

Configuring a custom WebBindingInitializer

To externalize data binding initialization, you can provide a custom implementation of the

WebBindingInitializer interface, which you then enable by supplying a custom bean configuration

for an AnnotationMethodHandlerAdapter, thus overriding the default configuration.

The following example from the PetClinic application shows a

configuration using a custom implementation of the WebBindingInitializer

interface, org.springframework.samples.petclinic.web.ClinicBindingInitializer,

which configures PropertyEditors required by several of the PetClinic controllers.

</property>

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 465

@InitBinder methods can also be defined in an @ControllerAdvice-annotated class in which case

they apply to matching controllers. This provides an alternative to using a WebBindingInitializer.

See the the section called “Advising controllers with the @ControllerAdvice annotation” section for

more details.

Support for the Last-Modified Response Header To Facilitate Content Caching

An @RequestMapping method may wish to support 'Last-Modified' HTTP requests, as defined in

the contract for the Servlet API’s getLastModified method, to facilitate content caching. This involves

calculating a lastModified long value for a given request, comparing it against the 'If-Modified-

Since' request header value, and potentially returning a response with status code 304 (Not Modified).

An annotated controller method can achieve that as follows:

@RequestMapping

public String myHandleMethod(WebRequest webRequest, Model model) {

long lastModified = // 1. application-specific calculation

if (request.checkNotModified(lastModified)) {

// 2. shortcut exit - no further processing necessary

return null;

}

// 3. or otherwise further request processing, actually preparing content

model.addAttribute(...);

return "myViewName";

}

There are two key elements to note: calling request.checkNotModified(lastModified) and

returning null. The former sets the response status to 304 before it returns true. The latter, in

combination with the former, causes Spring MVC to do no further processing of the request.

Advising controllers with the @ControllerAdvice annotation

The @ControllerAdvice annotation is a component annotation allowing implementation classes

to be auto-detected through classpath scanning. It is automatically enabled when using the MVC

namespace or the MVC Java config.

Classes annotated with @ControllerAdvice can contain @ExceptionHandler, @InitBinder,

and @ModelAttribute annotated methods, and these methods will apply to @RequestMapping

methods across all controller hierarchies as opposed to the controller hierarchy within which they are

declared.

The @ControllerAdvice annotation can also target a subset of controllers with its attributes:

// Target all Controllers annotated with @RestController

@ControllerAdvice(annotations = RestController.class)

public class AnnotationAdvice {}

// Target all Controllers within specific packages

@ControllerAdvice("org.example.controllers")

public class BasePackageAdvice {}

// Target all Controllers assignable to specific classes

@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})

public class AssignableTypesAdvice {}

Check out the @ControllerAdvice documentation for more details.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 466

Jackson Serialization View Support

It can sometimes be useful to filter contextually the object that will be serialized to the HTTP response

body. In order to provide such capability, Spring MVC has built-in support for rendering with Jackson’s

Serialization Views.

To use it with @ResponseBody controller method or methods return ResponseEntity, simply add

the @JsonView annotation:

@RestController

public class UserController {

@RequestMapping(value = "/user", method = RequestMethod.GET)

@JsonView(User.WithoutPasswordView.class)

public User getUser() {

return new User("eric", "7!jd#h23");

}

public class User {

public interface WithoutPasswordView {};

public interface WithPasswordView extends WithoutPasswordView {};

private String username;

private String password;

public User() {

}

public User(String username, String password) {

this.username = username;

this.password = password;

}

@JsonView(WithoutPasswordView.class)

public String getUsername() {

return this.username;

}

@JsonView(WithPasswordView.class)

public String getPassword() {

return this.password;

}

For controllers relying on view resolution, simply add the serialization view class to the model:

@Controller

public class UserController extends AbstractController {

@RequestMapping(value = "/user", method = RequestMethod.GET)

public String getUser(Model model) {

model.addAttribute("user", new User("eric", "7!jd#h23"));

model.addAttribute(JsonView.class.getName(), User.WithoutPasswordView.class);

return "userView";

}

Jackson JSONP Support

In order to enable JSONP support for @ResponseBody and ResponseEntity methods, declare an

@ControllerAdvice bean that extends AbstractJsonpResponseBodyAdvice as shown below

where the constructor argument indicates the JSONP query parameter name(s):

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 467

@ControllerAdvice

public class JsonpAdvice extends AbstractJsonpResponseBodyAdvice {

public JsonpAdvice() {

super("callback");

}

For controllers relying on view resolution, JSONP is automatically enabled when the request

has a query parameter named jsonp or callback. Those names can be customized through

jsonpParameterNames property.

Asynchronous Request Processing

Spring MVC 3.2 introduced Servlet 3 based asynchronous request processing. Instead of returning

a value, as usual, a controller method can now return a java.util.concurrent.Callable and

produce the return value from a separate thread. Meanwhile the main Servlet container thread is

released and allowed to process other requests. Spring MVC invokes the Callable in a separate

thread with the help of a TaskExecutor and when the Callable returns, the request is dispatched

back to the Servlet container to resume processing with the value returned by the Callable. Here is

an example controller method:

@RequestMapping(method=RequestMethod.POST)

public Callable<String> processUpload(final MultipartFile file) {

return new Callable<String>() {

public String call() throws Exception {

// ...

return "someView";

}

};

}

A second option is for the controller to return an instance of DeferredResult. In this case the return

value will also be produced from a separate thread. However, that thread is not known to Spring MVC.

For example the result may be produced in response to some external event such as a JMS message,

a scheduled task, etc. Here is an example controller method:

@RequestMapping("/quotes")

@ResponseBody

public DeferredResult<String> quotes() {

DeferredResult<String> deferredResult = new DeferredResult<String>();

// Save the deferredResult in in-memory queue ...

return deferredResult;

}

// In some other thread...

deferredResult.setResult(data);

This may be difficult to understand without any knowledge of the Servlet 3 async processing feature. It

would certainly help to read up on it. At a very minimum consider the following basic facts:

• A ServletRequest can be put in asynchronous mode by calling request.startAsync(). The

main effect of doing so is that the Servlet, as well as any Filters, can exit but the response will remain

open allowing some other thread to complete processing.

• The call to request.startAsync() returns an AsyncContext, which can be used for further

control over async processing. For example it provides the method dispatch, which can be called

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 468

from an application thread in order to "dispatch" the request back to the Servlet container. An async

dispatch is similar to a forward except it is made from one (application) thread to another (Servlet

container) thread whereas a forward occurs synchronously in the same (Servlet container) thread.

•ServletRequest provides access to the current DispatcherType, which can be used to

distinguish if a Servlet or a Filter is processing on the initial request processing thread and when

it is processing in an async dispatch.

With the above in mind, the following is the sequence of events for async request processing with a

Callable: (1) Controller returns a Callable, (2) Spring MVC starts async processing and submits

the Callable to a TaskExecutor for processing in a separate thread, (3) the DispatcherServlet

and all Filter’s exit the request processing thread but the response remains open, (4) the Callable

produces a result and Spring MVC dispatches the request back to the Servlet container, (5) the

DispatcherServlet is invoked again and processing resumes with the asynchronously produced

result from the Callable. The exact sequencing of (2), (3), and (4) may vary depending on the speed

of execution of the concurrent threads.

The sequence of events for async request processing with a DeferredResult is the same in

principal except it’s up to the application to produce the asynchronous result from some thread:

(1) Controller returns a DeferredResult and saves it in some in-memory queue or list where it

can be accessed, (2) Spring MVC starts async processing, (3) the DispatcherServlet and all

configured Filter’s exit the request processing thread but the response remains open, (4) the application

sets the DeferredResult from some thread and Spring MVC dispatches the request back to the

Servlet container, (5) the DispatcherServlet is invoked again and processing resumes with the

asynchronously produced result.

Explaining the motivation for async request processing and when or why to use it are beyond the scope

of this document. For further information you may wish to read this blog post series.

Exception Handling for Async Requests

What happens if a Callable returned from a controller method raises an Exception while being

executed? The effect is similar to what happens when any controller method raises an exception. It is

handled by a matching @ExceptionHandler method in the same controller or by one of the configured

HandlerExceptionResolver instances.

Note

Under the covers, when a Callable raises an Exception, Spring MVC still dispatches

to the Servlet container to resume processing. The only difference is that the result of

executing the Callable is an Exception that must be processed with the configured

HandlerExceptionResolver instances.

When using a DeferredResult, you have a choice of calling its setErrorResult(Object) method

and provide an Exception or any other Object you’d like to use as the result. If the result is an

Exception, it will be processed with a matching @ExceptionHandler method in the same controller

or with any configured HandlerExceptionResolver instance.

Intercepting Async Requests

An existing HandlerInterceptor can implement AsyncHandlerInterceptor, which provides

one additional method afterConcurrentHandlingStarted. It is invoked after async

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 469

processing starts and when the initial request processing thread is being exited. See the

AsyncHandlerInterceptor javadocs for more details on that.

Further options for async request lifecycle callbacks are provided directly on DeferredResult, which

has the methods onTimeout(Runnable) and onCompletion(Runnable). Those are called when

the async request is about to time out or has completed respectively. The timeout event can be handled

by setting the DeferredResult to some value. The completion callback however is final and the result

can no longer be set.

Similar callbacks are also available with a Callable. However, you will need to wrap the Callable

in an instance of WebAsyncTask and then use that to register the timeout and completion callbacks.

Just like with DeferredResult, the timeout event can be handled and a value can be returned while

the completion event is final.

You can also register a CallableProcessingInterceptor or a

DeferredResultProcessingInterceptor globally through the MVC Java config or the MVC

namespace. Those interceptors provide a full set of callbacks and apply every time a Callable or a

DeferredResult is used.

Configuration for Async Request Processing

Servlet 3 Async Config

To use Servlet 3 async request processing, you need to update web.xml to version 3.0:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"

version="3.0">

...

</web-app>

The DispatcherServlet and any Filter configuration need to have the <async-

supported>true</async-supported> sub-element. Additionally, any Filter that also needs to

get involved in async dispatches should also be configured to support the ASYNC dispatcher type. Note

that it is safe to enable the ASYNC dispatcher type for all filters provided with the Spring Framework

since they will not get involved in async dispatches unless needed.

Warning

Note that for some Filters it is absolutely critical to ensure they are mapped to

be invoked during asynchronous dispatches. For example if a filter such as the

OpenEntityManagerInViewFilter is responsible for releasing database connection

resources and must be invoked at the end of an async request.

Below is an example of a propertly configured filter:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 470

<web-app xmlns="http://java.sun.com/xml/ns/javaee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"

version="3.0">

<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>

<filter-class>org.springframework.~.OpenEntityManagerInViewFilter</filter-class>

<async-supported>true</async-supported>

</filter>

<filter-mapping>

<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>

<url-pattern>/*</url-pattern>

<dispatcher>REQUEST</dispatcher>

<dispatcher>ASYNC</dispatcher>

</filter-mapping>

</web-app>

If using Servlet 3, Java based configuration, e.g. via WebApplicationInitializer, you’ll also need

to set the "asyncSupported" flag as well as the ASYNC dispatcher type just like with web.xml. To

simplify all this configuration, consider extending AbstractDispatcherServletInitializer or

AbstractAnnotationConfigDispatcherServletInitializer, which automatically set those

options and make it very easy to register Filter instances.

Spring MVC Async Config

The MVC Java config and the MVC namespace both provide options for configuring async request

processing. WebMvcConfigurer has the method configureAsyncSupport while <mvc:annotation-

driven> has an <async-support> sub-element.

Those allow you to configure the default timeout value to use for async requests, which if not

set depends on the underlying Servlet container (e.g. 10 seconds on Tomcat). You can also

configure an AsyncTaskExecutor to use for executing Callable instances returned from controller

methods. It is highly recommended to configure this property since by default Spring MVC uses

SimpleAsyncTaskExecutor. The MVC Java config and the MVC namespace also allow you

to register CallableProcessingInterceptor and DeferredResultProcessingInterceptor

instances.

If you need to override the default timeout value for a specific DeferredResult, you can do so by

using the appropriate class constructor. Similarly, for a Callable, you can wrap it in a WebAsyncTask

and use the appropriate class constructor to customize the timeout value. The class constructor of

WebAsyncTask also allows providing an AsyncTaskExecutor.

Testing Controllers

The spring-test module offers first class support for testing annotated controllers. See the section

called “Spring MVC Test Framework”.

17.4 Handler mappings

In previous versions of Spring, users were required to define one or more HandlerMapping

beans in the web application context to map incoming web requests to appropriate handlers.

With the introduction of annotated controllers, you generally don’t need to do that because the

RequestMappingHandlerMapping automatically looks for @RequestMapping annotations on all

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 471

@Controller beans. However, do keep in mind that all HandlerMapping classes extending from

AbstractHandlerMapping have the following properties that you can use to customize their

behavior:

•interceptors List of interceptors to use. HandlerInterceptors are discussed in the section

called “Intercepting requests with a HandlerInterceptor”.

•defaultHandler Default handler to use, when this handler mapping does not result in a matching

handler.

•order Based on the value of the order property (see the org.springframework.core.Ordered

interface), Spring sorts all handler mappings available in the context and applies the first matching

handler.

•alwaysUseFullPath If true , Spring uses the full path within the current Servlet context to find an

appropriate handler. If false (the default), the path within the current Servlet mapping is used. For

example, if a Servlet is mapped using /testing/* and the alwaysUseFullPath property is set to

true, /testing/viewPage.html is used, whereas if the property is set to false, /viewPage.html

is used.

•urlDecode Defaults to true, as of Spring 2.5. If you prefer to compare encoded paths, set this flag

to false. However, the HttpServletRequest always exposes the Servlet path in decoded form.

Be aware that the Servlet path will not match when compared with encoded paths.

The following example shows how to configure an interceptor:

<beans>

</property>

</bean>

<beans>

Intercepting requests with a HandlerInterceptor

Spring’s handler mapping mechanism includes handler interceptors, which are useful when you want

to apply specific functionality to certain requests, for example, checking for a principal.

Interceptors located in the handler mapping must implement HandlerInterceptor from

the org.springframework.web.servlet package. This interface defines three methods:

preHandle(..) is called before the actual handler is executed; postHandle(..) is called after

the handler is executed; and afterCompletion(..) is called after the complete request has

finished. These three methods should provide enough flexibility to do all kinds of preprocessing and

postprocessing.

The preHandle(..) method returns a boolean value. You can use this method to break or continue

the processing of the execution chain. When this method returns true, the handler execution chain

will continue; when it returns false, the DispatcherServlet assumes the interceptor itself has taken

care of requests (and, for example, rendered an appropriate view) and does not continue executing the

other interceptors and the actual handler in the execution chain.

Interceptors can be configured using the interceptors property, which is present on all

HandlerMapping classes extending from AbstractHandlerMapping. This is shown in the example

below:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 472

<beans>

<bean id="handlerMapping"

class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping">

<list>

</list>

</property>

</bean>

<bean id="officeHoursInterceptor"

class="samples.TimeBasedAccessInterceptor">

</bean>

<beans>

package samples;

public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter {

private int openingTime;

private int closingTime;

public void setOpeningTime(int openingTime) {

this.openingTime = openingTime;

}

public void setClosingTime(int closingTime) {

this.closingTime = closingTime;

}

public boolean preHandle(HttpServletRequest request, HttpServletResponse response,

Object handler) throws Exception {

Calendar cal = Calendar.getInstance();

int hour = cal.get(HOUR_OF_DAY);

if (openingTime <= hour && hour < closingTime) {

return true;

}

response.sendRedirect("http://host.com/outsideOfficeHours.html");

return false;

}

Any request handled by this mapping is intercepted by the TimeBasedAccessInterceptor. If the

current time is outside office hours, the user is redirected to a static HTML file that says, for example,

you can only access the website during office hours.

Note

When using the RequestMappingHandlerMapping the actual handler is an instance of

HandlerMethod which identifies the specific controller method that will be invoked.

As you can see, the Spring adapter class HandlerInterceptorAdapter makes it easier to extend

the HandlerInterceptor interface.

Tip

In the example above, the configured interceptor will apply to all requests handled with annotated

controller methods. If you want to narrow down the URL paths to which an interceptor applies,

you can use the MVC namespace or the MVC Java config, or declare bean instances of type

MappedInterceptor to do that. See the section called “Enabling the MVC Java Config or the

MVC XML Namespace”.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 473

Note that the postHandle method of HandlerInterceptor is not always ideally suited for use

with @ResponseBody and ResponseEntity methods. In such cases an HttpMessageConverter

writes to and commits the response before postHandle is called which makes it impossible

to change the response, for example to add a header. Instead an application can implement

ResponseBodyAdvice and either declare it as an @ControllerAdvice bean or configure it directly

on RequestMappingHandlerAdapter.

17.5 Resolving views

All MVC frameworks for web applications provide a way to address views. Spring provides view

resolvers, which enable you to render models in a browser without tying you to a specific view

technology. Out of the box, Spring enables you to use JSPs, Velocity templates and XSLT views, for

example. See Chapter 18, View technologies for a discussion of how to integrate and use a number

of disparate view technologies.

The two interfaces that are important to the way Spring handles views are ViewResolver and View.

The ViewResolver provides a mapping between view names and actual views. The View interface

addresses the preparation of the request and hands the request over to one of the view technologies.

Resolving views with the ViewResolver interface

As discussed in Section 17.3, “Implementing Controllers”, all handler methods in the Spring Web MVC

controllers must resolve to a logical view name, either explicitly (e.g., by returning a String, View, or

ModelAndView) or implicitly (i.e., based on conventions). Views in Spring are addressed by a logical

view name and are resolved by a view resolver. Spring comes with quite a few view resolvers. This

table lists most of them; a couple of examples follow.

Table 17.3. View resolvers

ViewResolver Description

AbstractCachingViewResolver Abstract view resolver that caches views. Often

views need preparation before they can be used;

extending this view resolver provides caching.

XmlViewResolver Implementation of ViewResolver that accepts

a configuration file written in XML with the same

DTD as Spring’s XML bean factories. The default

configuration file is /WEB-INF/views.xml.

ResourceBundleViewResolver Implementation of ViewResolver that uses

bean definitions in a ResourceBundle,

specified by the bundle base name. Typically

you define the bundle in a properties file,

located in the classpath. The default file name is

views.properties.

UrlBasedViewResolver Simple implementation of the ViewResolver

interface that effects the direct resolution of

logical view names to URLs, without an explicit

mapping definition. This is appropriate if your

logical names match the names of your view

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 474

ViewResolver Description

resources in a straightforward manner, without

the need for arbitrary mappings.

InternalResourceViewResolver Convenient subclass of

UrlBasedViewResolver that supports

InternalResourceView (in effect, Servlets

and JSPs) and subclasses such as JstlView

and TilesView. You can specify the view

class for all views generated by this resolver

by using setViewClass(..). See the

UrlBasedViewResolver javadocs for details.

VelocityViewResolver /

FreeMarkerViewResolver

Convenient subclass of

UrlBasedViewResolver that supports

VelocityView (in effect, Velocity templates)

or FreeMarkerView ,respectively, and custom

subclasses of them.

ContentNegotiatingViewResolver Implementation of the ViewResolver interface

that resolves a view based on the request file

name or Accept header. See the section called

“ContentNegotiatingViewResolver”.

As an example, with JSP as a view technology, you can use the UrlBasedViewResolver. This view

resolver translates a view name to a URL and hands the request over to the RequestDispatcher to

render the view.

<bean id="viewResolver"

class="org.springframework.web.servlet.view.UrlBasedViewResolver">

</bean>

When returning test as a logical view name, this view resolver forwards the request to the

RequestDispatcher that will send the request to /WEB-INF/jsp/test.jsp.

When you combine different view technologies in a web application, you can use the

ResourceBundleViewResolver:

<bean id="viewResolver"

class="org.springframework.web.servlet.view.ResourceBundleViewResolver">

</bean>

The ResourceBundleViewResolver inspects the ResourceBundle identified by the basename,

and for each view it is supposed to resolve, it uses the value of the property [viewname].(class) as

the view class and the value of the property [viewname].url as the view url. Examples can be found

in the next chapter which covers view technologies. As you can see, you can identify a parent view, from

which all views in the properties file "extend". This way you can specify a default view class, for example.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 475

Note

Subclasses of AbstractCachingViewResolver cache view instances that they resolve.

Caching improves performance of certain view technologies. It’s possible to turn off the cache by

setting the cache property to false. Furthermore, if you must refresh a certain view at runtime

(for example when a Velocity template is modified), you can use the removeFromCache(String

viewName, Locale loc) method.

Chaining ViewResolvers

Spring supports multiple view resolvers. Thus you can chain resolvers and, for example, override specific

views in certain circumstances. You chain view resolvers by adding more than one resolver to your

application context and, if necessary, by setting the order property to specify ordering. Remember, the

higher the order property, the later the view resolver is positioned in the chain.

In the following example, the chain of view resolvers consists of two resolvers, an

InternalResourceViewResolver, which is always automatically positioned as the last resolver in

the chain, and an XmlViewResolver for specifying Excel views. Excel views are not supported by the

InternalResourceViewResolver.

</bean>

</bean>

<beans>

</beans>

If a specific view resolver does not result in a view, Spring examines the context for other view resolvers.

If additional view resolvers exist, Spring continues to inspect them until a view is resolved. If no view

resolver returns a view, Spring throws a ServletException.

The contract of a view resolver specifies that a view resolver can return null to indicate the view could not

be found. Not all view resolvers do this, however, because in some cases, the resolver simply cannot

detect whether or not the view exists. For example, the InternalResourceViewResolver uses the

RequestDispatcher internally, and dispatching is the only way to figure out if a JSP exists, but this

action can only execute once. The same holds for the VelocityViewResolver and some others.

Check the javadocs of the specific view resolver to see whether it reports non-existing views. Thus,

putting an InternalResourceViewResolver in the chain in a place other than the last results in the

chain not being fully inspected, because the InternalResourceViewResolver will always return

a view!

Redirecting to views

As mentioned previously, a controller typically returns a logical view name, which a view

resolver resolves to a particular view technology. For view technologies such as JSPs that are

processed through the Servlet or JSP engine, this resolution is usually handled through the

combination of InternalResourceViewResolver and InternalResourceView, which issues

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 476

an internal forward or include via the Servlet API’s RequestDispatcher.forward(..) method or

RequestDispatcher.include() method. For other view technologies, such as Velocity, XSLT, and

so on, the view itself writes the content directly to the response stream.

It is sometimes desirable to issue an HTTP redirect back to the client, before the view is rendered. This

is desirable, for example, when one controller has been called with POST data, and the response is

actually a delegation to another controller (for example on a successful form submission). In this case,

a normal internal forward will mean that the other controller will also see the same POST data, which is

potentially problematic if it can confuse it with other expected data. Another reason to perform a redirect

before displaying the result is to eliminate the possibility of the user submitting the form data multiple

times. In this scenario, the browser will first send an initial POST; it will then receive a response to redirect

to a different URL; and finally the browser will perform a subsequent GET for the URL named in the

redirect response. Thus, from the perspective of the browser, the current page does not reflect the result

of a POST but rather of a GET. The end effect is that there is no way the user can accidentally re- POST

the same data by performing a refresh. The refresh forces a GET of the result page, not a resend of

the initial POST data.

RedirectView

One way to force a redirect as the result of a controller response is for the controller to create and

return an instance of Spring’s RedirectView. In this case, DispatcherServlet does not use the

normal view resolution mechanism. Rather because it has been given the (redirect) view already, the

DispatcherServlet simply instructs the view to do its work.

The RedirectView issues an HttpServletResponse.sendRedirect() call that returns to the

client browser as an HTTP redirect. By default all model attributes are considered to be exposed as

URI template variables in the redirect URL. Of the remaining attributes those that are primitive types or

collections/arrays of primitive types are automatically appended as query parameters.

Appending primitive type attributes as query parameters may be the desired result if a model instance

was prepared specifically for the redirect. However, in annotated controllers the model may contain

additional attributes added for rendering purposes (e.g. drop-down field values). To avoid the possibility

of having such attributes appear in the URL an annotated controller can declare an argument of type

RedirectAttributes and use it to specify the exact attributes to make available to RedirectView.

If the controller method decides to redirect, the content of RedirectAttributes is used. Otherwise

the content of the model is used.

Note that URI template variables from the present request are automatically made available when

expanding a redirect URL and do not need to be added explicitly neither through Model nor

RedirectAttributes. For example:

@RequestMapping(value = "/files/{path}", method = RequestMethod.POST)

public String upload(...) {

// ...

return "redirect:files/{path}";

}

If you use RedirectView and the view is created by the controller itself, it is recommended that you

configure the redirect URL to be injected into the controller so that it is not baked into the controller but

configured in the context along with the view names. The next section discusses this process.

The redirect: prefix

While the use of RedirectView works fine, if the controller itself creates the RedirectView, there is

no avoiding the fact that the controller is aware that a redirection is happening. This is really suboptimal

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 477

and couples things too tightly. The controller should not really care about how the response gets handled.

In general it should operate only in terms of view names that have been injected into it.

The special redirect: prefix allows you to accomplish this. If a view name is returned that has the

prefix redirect:, the UrlBasedViewResolver (and all subclasses) will recognize this as a special

indication that a redirect is needed. The rest of the view name will be treated as the redirect URL.

The net effect is the same as if the controller had returned a RedirectView, but now the controller

itself can simply operate in terms of logical view names. A logical view name such as redirect:/

myapp/some/resource will redirect relative to the current Servlet context, while a name such as

redirect:http://myhost.com/some/arbitrary/path will redirect to an absolute URL.

The forward: prefix

It is also possible to use a special forward: prefix for view names that are ultimately resolved

by UrlBasedViewResolver and subclasses. This creates an InternalResourceView (which

ultimately does a RequestDispatcher.forward()) around the rest of the view name, which is

considered a URL. Therefore, this prefix is not useful with InternalResourceViewResolver and

InternalResourceView (for JSPs for example). But the prefix can be helpful when you are primarily

using another view technology, but still want to force a forward of a resource to be handled by the

Servlet/JSP engine. (Note that you may also chain multiple view resolvers, instead.)

As with the redirect: prefix, if the view name with the forward: prefix is injected into the controller,

the controller does not detect that anything special is happening in terms of handling the response.

ContentNegotiatingViewResolver

The ContentNegotiatingViewResolver does not resolve views itself but rather delegates to other

view resolvers, selecting the view that resembles the representation requested by the client. Two

strategies exist for a client to request a representation from the server:

• Use a distinct URI for each resource, typically by using a different file extension in the

URI. For example, the URI http://www.example.com/users/fred.pdf requests a PDF

representation of the user fred, and http://www.example.com/users/fred.xml requests an

XML representation.

• Use the same URI for the client to locate the resource, but set the Accept HTTP request

header to list the media types that it understands. For example, an HTTP request for http://

www.example.com/users/fred with an Accept header set to application/pdf requests

a PDF representation of the user fred, while http://www.example.com/users/fred with an

Accept header set to text/xml requests an XML representation. This strategy is known as content

negotiation.

Note

One issue with the Accept header is that it is impossible to set it in a web browser within HTML.

For example, in Firefox, it is fixed to:

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8

For this reason it is common to see the use of a distinct URI for each representation when

developing browser based web applications.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 478

To support multiple representations of a resource, Spring provides the

ContentNegotiatingViewResolver to resolve a view based on the file extension or Accept

header of the HTTP request. ContentNegotiatingViewResolver does not perform the view

resolution itself but instead delegates to a list of view resolvers that you specify through the bean property

ViewResolvers.

The ContentNegotiatingViewResolver selects an appropriate View to handle the request by

comparing the request media type(s) with the media type (also known as Content-Type) supported by

the View associated with each of its ViewResolvers. The first View in the list that has a compatible

Content-Type returns the representation to the client. If a compatible view cannot be supplied by

the ViewResolver chain, then the list of views specified through the DefaultViews property will

be consulted. This latter option is appropriate for singleton Views that can render an appropriate

representation of the current resource regardless of the logical view name. The Accept header may

include wild cards, for example text/*, in which case a View whose Content-Type was text/xml

is a compatible match.

To support the resolution of a view based on a file extension, use the

ContentNegotiatingViewResolver bean property mediaTypes to specify a mapping of file

extensions to media types. For more information on the algorithm used to determine the request media

type, refer to the API documentation for ContentNegotiatingViewResolver.

Here is an example configuration of a ContentNegotiatingViewResolver:

<map>

</map>

</property>

<list>

</bean>

</list>

</property>

<list>

</list>

</property>

</bean>

The InternalResourceViewResolver handles the translation of view names and JSP pages, while

the BeanNameViewResolver returns a view based on the name of a bean. (See "Resolving views

with the ViewResolver interface" for more details on how Spring looks up and instantiates a view.) In

this example, the content bean is a class that inherits from AbstractAtomFeedView, which returns

an Atom RSS feed. For more information on creating an Atom Feed representation, see the section

Atom Views.

In the above configuration, if a request is made with an .html extension, the view resolver looks for a

view that matches the text/html media type. The InternalResourceViewResolver provides the

matching view for text/html. If the request is made with the file extension .atom, the view resolver

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 479

looks for a view that matches the application/atom+xml media type. This view is provided by the

BeanNameViewResolver that maps to the SampleContentAtomView if the view name returned

is content. If the request is made with the file extension .json, the MappingJackson2JsonView

instance from the DefaultViews list will be selected regardless of the view name. Alternatively, client

requests can be made without a file extension but with the Accept header set to the preferred media-

type, and the same resolution of request to views would occur.

Note

If ContentNegotiatingViewResolver's list of ViewResolvers is not configured explicitly, it

automatically uses any ViewResolvers defined in the application context.

The corresponding controller code that returns an Atom RSS feed for a URI of the form

http://localhost/content.atom or http://localhost/content with an Accept header of

application/atom+xml is shown below.

@Controller

public class ContentController {

private List<SampleContent> contentList = new ArrayList<SampleContent>();

@RequestMapping(value="/content", method=RequestMethod.GET)

public ModelAndView getContent() {

ModelAndView mav = new ModelAndView();

mav.setViewName("content");

mav.addObject("sampleContentList", contentList);

return mav;

}

17.6 Using flash attributes

Flash attributes provide a way for one request to store attributes intended for use in another. This is

most commonly needed when redirecting — for example, the Post/Redirect/Get pattern. Flash attributes

are saved temporarily before the redirect (typically in the session) to be made available to the request

after the redirect and removed immediately.

Spring MVC has two main abstractions in support of flash attributes. FlashMap is used to hold flash

attributes while FlashMapManager is used to store, retrieve, and manage FlashMap instances.

Flash attribute support is always "on" and does not need to enabled explicitly although if not used, it never

causes HTTP session creation. On each request there is an "input" FlashMap with attributes passed

from a previous request (if any) and an "output" FlashMap with attributes to save for a subsequent

request. Both FlashMap instances are accessible from anywhere in Spring MVC through static methods

in RequestContextUtils.

Annotated controllers typically do not need to work with FlashMap directly. Instead an

@RequestMapping method can accept an argument of type RedirectAttributes and use it to

add flash attributes for a redirect scenario. Flash attributes added via RedirectAttributes are

automatically propagated to the "output" FlashMap. Similarly after the redirect attributes from the "input"

FlashMap are automatically added to the Model of the controller serving the target URL.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 480

Matching requests to flash attributes

The concept of flash attributes exists in many other Web frameworks and has proven to be exposed

sometimes to concurrency issues. This is because by definition flash attributes are to be stored

until the next request. However the very "next" request may not be the intended recipient but

another asynchronous request (e.g. polling or resource requests) in which case the flash attributes

are removed too early.

To reduce the possibility of such issues, RedirectView automatically "stamps" FlashMap

instances with the path and query parameters of the target redirect URL. In turn the default

FlashMapManager matches that information to incoming requests when looking up the "input"

FlashMap.

This does not eliminate the possibility of a concurrency issue entirely but nevertheless reduces

it greatly with information that is already available in the redirect URL. Therefore the use of flash

attributes is recommended mainly for redirect scenarios .

17.7 Building URIs

Spring MVC provides a mechanism for building and encoding a URI using UriComponentsBuilder

and UriComponents.

For example you can expand and encode a URI template string:

UriComponents uriComponents = UriComponentsBuilder.fromUriString(

"http://example.com/hotels/{hotel}/bookings/{booking}").build();

URI uri = uriComponents.expand("42", "21").encode().toUri();

Note that UriComponents is immutable and the expand() and encode() operations return new

instances if necessary.

You can also expand and encode using individual URI components:

UriComponents uriComponents = UriComponentsBuilder.newInstance()

.scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build()

.expand("42", "21")

.encode();

In a Servlet environment the ServletUriComponentsBuilder sub-class provides static factory

methods to copy available URL information from a Servlet requests:

HttpServletRequest request = ...

// Re-use host, scheme, port, path and query string

// Replace the "accountId" query param

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request)

.replaceQueryParam("accountId", "{id}").build()

.expand("123")

.encode();

Alternatively, you may choose to copy a subset of the available information up to and including the

context path:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 481

// Re-use host, port and context path

// Append "/accounts" to the path

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request)

.path("/accounts").build()

Or in cases where the DispatcherServlet is mapped by name (e.g. /main/*), you can also have

the literal part of the servlet mapping included:

// Re-use host, port, context path

// Append the literal part of the servlet mapping to the path

// Append "/accounts" to the path

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request)

.path("/accounts").build()

Building URIs to Controllers and methods

Spring MVC provides another mechanism for building and encoding URIs that link to

Controllers and methods defined within an application. MvcUriComponentsBuilder extends

UriComponentsBuilder and provides such possibilities.

Given this Controller:

@Controller

@RequestMapping("/hotels/{hotel}")

public class BookingController {

@RequestMapping("/bookings/{booking}")

public String getBooking(@PathVariable Long booking) {

// ...

}

and using the MvcUriComponentsBuilder, the previous example is now:

UriComponents uriComponents = MvcUriComponentsBuilder

.fromMethodName(BookingController.class, "getBooking",21).buildAndExpand(42);

URI uri = uriComponents.encode().toUri();

The MvcUriComponentsBuilder can also create "mock Controllers", thus enabling to create URIs

by coding against the actual Controller’s API:

UriComponents uriComponents = MvcUriComponentsBuilder

.fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

URI uri = uriComponents.encode().toUri();

Building URIs to Controllers and methods from views

It is also useful to build links to annotated controllers from views (e.g. JSP). This can be done

through a method on MvcUriComponentsBuilder which refers to mappings by name called

fromMappingName.

As of 4.1 every @RequestMapping is assigned a default name based on the capital

letters of the class and the full method name. For example, the method getFoo

in class FooController is assigned the name "FC#getFoo". This naming strategy is

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 482

pluggable by implementing HandlerMethodMappingNamingStrategy and configuring it on your

RequestMappingHandlerMapping. Furthermore the @RequestMapping annotation includes a

name attribute that can be used to override the default strategy.

Note

The assigned request mapping names are logged at TRACE level on startup.

The Spring JSP tag library provides a function called mvcUrl that can be used to prepare links to

controller methods based on this mechanism.

For example given:

@RequestMapping("/people/{id}/addresses")

public class MyController {

@RequestMapping("/{country}")

public HttpEntity getAddress(@PathVariable String country) { ... }

}

The following JSP code can prepare a link:

<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %>

...

<a href="${s:mvcUrl(PC#getPerson).arg(0,123).build()}">Get Person</a>

17.8 Using locales

Most parts of Spring’s architecture support internationalization, just as the Spring web MVC framework

does. DispatcherServlet enables you to automatically resolve messages using the client’s locale.

This is done with LocaleResolver objects.

When a request comes in, the DispatcherServlet looks for a locale resolver, and if it finds one it

tries to use it to set the locale. Using the RequestContext.getLocale() method, you can always

retrieve the locale that was resolved by the locale resolver.

In addition to automatic locale resolution, you can also attach an interceptor to the handler mapping

(see the section called “Intercepting requests with a HandlerInterceptor” for more information on handler

mapping interceptors) to change the locale under specific circumstances, for example, based on a

parameter in the request.

Locale resolvers and interceptors are defined in the org.springframework.web.servlet.i18n

package and are configured in your application context in the normal way. Here is a selection of the

locale resolvers included in Spring.

Obtaining Time Zone Information

In addition to obtaining the client’s locale, it is often useful to know their time zone. The

LocaleContextResolver interface offers an extension to LocaleResolver that allows resolvers

to provide a richer LocaleContext, which may include time zone information.

When available, the user’s TimeZone can be obtained using the RequestContext.getTimeZone()

method. Time zone information will automatically be used by Date/Time Converter and Formatter

objects registered with Spring’s ConversionService.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 483

AcceptHeaderLocaleResolver

This locale resolver inspects the accept-language header in the request that was sent by the client

(e.g., a web browser). Usually this header field contains the locale of the client’s operating system. Note

that this resolver does not support time zone information.

CookieLocaleResolver

This locale resolver inspects a Cookie that might exist on the client to see if a Locale or TimeZone

is specified. If so, it uses the specified details. Using the properties of this locale resolver, you can

specify the name of the cookie as well as the maximum age. Find below an example of defining a

CookieLocaleResolver.

</bean>

Table 17.4. CookieLocaleResolver properties

Property Default Description

cookieName classname +

LOCALE

The name of the cookie

cookieMaxAge Integer.MAX_INTThe maximum time a cookie will stay persistent on the client. If -1

is specified, the cookie will not be persisted; it will only be available

until the client shuts down their browser.

cookiePath / Limits the visibility of the cookie to a certain part of your site. When

cookiePath is specified, the cookie will only be visible to that path

and the paths below it.

SessionLocaleResolver

The SessionLocaleResolver allows you to retrieve Locale and TimeZone from the session that

might be associated with the user’s request.

LocaleChangeInterceptor

You can enable changing of locales by adding the LocaleChangeInterceptor to one of the handler

mappings (see Section 17.4, “Handler mappings”). It will detect a parameter in the request and change

the locale. It calls setLocale() on the LocaleResolver that also exists in the context. The following

example shows that calls to all *.view resources containing a parameter named siteLanguage

will now change the locale. So, for example, a request for the following URL, http://www.sf.net/

home.view?siteLanguage=nl will change the site language to Dutch.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 484

<bean id="localeChangeInterceptor"

class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">

</bean>

<bean id="localeResolver"

class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/>

<bean id="urlMapping"

class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">

<list>

</list>

</property>

<value>/*/.view=someController</value>

</property>

</bean>

17.9 Using themes

Overview of themes

You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application,

thereby enhancing user experience. A theme is a collection of static resources, typically style sheets

and images, that affect the visual style of the application.

Defining themes

To use themes in your web application, you must set up an

implementation of the org.springframework.ui.context.ThemeSource interface.

The WebApplicationContext interface extends ThemeSource but delegates

its responsibilities to a dedicated implementation. By default the delegate

will be an org.springframework.ui.context.support.ResourceBundleThemeSource

implementation that loads properties files from the root of the classpath. To use a custom ThemeSource

implementation or to configure the base name prefix of the ResourceBundleThemeSource, you can

context automatically detects a bean with that name and uses it.

When using the ResourceBundleThemeSource, a theme is defined in a simple properties file. The

properties file lists the resources that make up the theme. Here is an example:

styleSheet=/themes/cool/style.css

background=/themes/cool/img/coolBg.jpg

The keys of the properties are the names that refer to the themed elements from view code. For

a JSP, you typically do this using the spring:theme custom tag, which is very similar to the

spring:message tag. The following JSP fragment uses the theme defined in the previous example

to customize the look and feel:

<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>

<html>

<head>

</head>

...

</body>

</html>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 485

By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result, the

properties files are loaded from the root of the classpath. Thus you would put the cool.properties

theme definition in a directory at the root of the classpath, for example, in /WEB-INF/classes.

The ResourceBundleThemeSource uses the standard Java resource bundle loading mechanism,

allowing for full internationalization of themes. For example, we could have a /WEB-INF/classes/

cool_nl.properties that references a special background image with Dutch text on it.

Theme resolvers

After you define themes, as in the preceding section, you decide which theme to use. The

DispatcherServlet will look for a bean named themeResolver to find out which ThemeResolver

implementation to use. A theme resolver works in much the same way as a LocaleResolver. It detects

the theme to use for a particular request and can also alter the request’s theme. The following theme

resolvers are provided by Spring:

Table 17.5. ThemeResolver implementations

Class Description

FixedThemeResolverSelects a fixed theme, set using the defaultThemeName property.

SessionThemeResolverThe theme is maintained in the user’s HTTP session. It only needs to be set

once for each session, but is not persisted between sessions.

CookieThemeResolverThe selected theme is stored in a cookie on the client.

Spring also provides a ThemeChangeInterceptor that allows theme changes on every request with

a simple request parameter.

17.10 Spring’s multipart (file upload) support

Introduction

Spring’s built-in multipart support handles file uploads in web applications. You enable

this multipart support with pluggable MultipartResolver objects, defined in the

org.springframework.web.multipart package. Spring provides one MultipartResolver

implementation for use with Commons FileUpload and another for use with Servlet 3.0 multipart request

parsing.

By default, Spring does no multipart handling, because some developers want to handle multiparts

themselves. You enable Spring multipart handling by adding a multipart resolver to the web application’s

context. Each request is inspected to see if it contains a multipart. If no multipart is found, the request

continues as expected. If a multipart is found in the request, the MultipartResolver that has been

declared in your context is used. After that, the multipart attribute in your request is treated like any

other attribute.

Using a MultipartResolver with Commons FileUpload

The following example shows how to use the CommonsMultipartResolver:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 486

<bean id="multipartResolver"

class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

</bean>

Of course you also need to put the appropriate jars in your classpath for the multipart resolver to work.

In the case of the CommonsMultipartResolver, you need to use commons-fileupload.jar.

When the Spring DispatcherServlet detects a multi-part request, it activates the resolver that

has been declared in your context and hands over the request. The resolver then wraps the current

HttpServletRequest into a MultipartHttpServletRequest that supports multipart file uploads.

Using the MultipartHttpServletRequest, you can get information about the multiparts contained

by this request and actually get access to the multipart files themselves in your controllers.

Using a MultipartResolver with Servlet 3.0

In order to use Servlet 3.0 based multipart parsing, you need to mark the

DispatcherServlet with a "multipart-config" section in web.xml, or with a

javax.servlet.MultipartConfigElement in programmatic Servlet registration, or in case of a

custom Servlet class possibly with a javax.servlet.annotation.MultipartConfig annotation

on your Servlet class. Configuration settings such as maximum sizes or storage locations need to be

applied at that Servlet registration level as Servlet 3.0 does not allow for those settings to be done from

the MultipartResolver.

Once Servlet 3.0 multipart parsing has been enabled in one of the above mentioned ways you can add

the StandardServletMultipartResolver to your Spring configuration:

<bean id="multipartResolver"

class="org.springframework.web.multipart.support.StandardServletMultipartResolver">

</bean>

Handling a file upload in a form

After the MultipartResolver completes its job, the request is processed like any other. First,

create a form with a file input that will allow the user to upload a form. The encoding attribute (

enctype="multipart/form-data") lets the browser know how to encode the form as multipart

request:

<html>

<head>

<title>Upload a file please</title>

</head>

<body>

<h1>Please upload a file</h1>

</form>

</body>

</html>

The next step is to create a controller that handles the file upload. This controller is very similar

to a normal annotated @Controller, except that we use MultipartHttpServletRequest or

MultipartFile in the method parameters:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 487

@Controller

public class FileUploadController {

@RequestMapping(value = "/form", method = RequestMethod.POST)

public String handleFormUpload(@RequestParam("name") String name,

@RequestParam("file") MultipartFile file) {

if (!file.isEmpty()) {

byte[] bytes = file.getBytes();

// store the bytes somewhere

return "redirect:uploadSuccess";

}

return "redirect:uploadFailure";

}

Note how the @RequestParam method parameters map to the input elements declared in the form. In

this example, nothing is done with the byte[], but in practice you can save it in a database, store it

on the file system, and so on.

When using Servlet 3.0 multipart parsing you can also use javax.servlet.http.Part for the

method parameter:

@Controller

public class FileUploadController {

@RequestMapping(value = "/form", method = RequestMethod.POST)

public String handleFormUpload(@RequestParam("name") String name,

@RequestParam("file") Part file) {

InputStream inputStream = file.getInputStream();

// store bytes from uploaded file somewhere

return "redirect:uploadSuccess";

}

Handling a file upload request from programmatic clients

Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. All

of the above examples and configuration apply here as well. However, unlike browsers that typically

submit files and simple form fields, a programmatic client can also send more complex data of a specific

content type — for example a multipart request with a file and second part with JSON formatted data:

POST /someUrl

Content-Type: multipart/mixed

--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp

Content-Disposition: form-data; name="meta-data"

Content-Type: application/json; charset=UTF-8

Content-Transfer-Encoding: 8bit

{

"name": "value"

}

--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp

Content-Disposition: form-data; name="file-data"; filename="file.properties"

Content-Type: text/xml

Content-Transfer-Encoding: 8bit

... File Data ...

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 488

You could access the part named "meta-data" with a @RequestParam("meta-data") String

metadata controller method argument. However, you would probably prefer to accept a strongly typed

object initialized from the JSON formatted data in the body of the request part, very similar to the way

@RequestBody converts the body of a non-multipart request to a target object with the help of an

HttpMessageConverter.

You can use the @RequestPart annotation instead of the @RequestParam annotation for

this purpose. It allows you to have the content of a specific multipart passed through an

HttpMessageConverter taking into consideration the 'Content-Type' header of the multipart:

@RequestMapping(value="/someUrl", method = RequestMethod.POST)

public String onSubmit(@RequestPart("meta-data") MetaData metadata,

@RequestPart("file-data") MultipartFile file) {

// ...

}

Notice how MultipartFile method arguments can be accessed with @RequestParam or with

@RequestPart interchangeably. However, the @RequestPart("meta-data") MetaData method

argument in this case is read as JSON content based on its 'Content-Type' header and converted

with the help of the MappingJackson2HttpMessageConverter.

17.11 Handling exceptions

HandlerExceptionResolver

Spring HandlerExceptionResolver implementations deal with unexpected exceptions that occur

during controller execution. A HandlerExceptionResolver somewhat resembles the exception

mappings you can define in the web application descriptor web.xml. However, they provide a more

flexible way to do so. For example they provide information about which handler was executing when

the exception was thrown. Furthermore, a programmatic way of handling exceptions gives you more

options for responding appropriately before the request is forwarded to another URL (the same end

result as when you use the Servlet specific exception mappings).

Besides implementing the HandlerExceptionResolver interface, which is only a matter

of implementing the resolveException(Exception, Handler) method and returning a

ModelAndView, you may also use the provided SimpleMappingExceptionResolver or create

@ExceptionHandler methods. The SimpleMappingExceptionResolver enables you to take the

class name of any exception that might be thrown and map it to a view name. This is functionally

equivalent to the exception mapping feature from the Servlet API, but it is also possible to implement

more finely grained mappings of exceptions from different handlers. The @ExceptionHandler

annotation on the other hand can be used on methods that should be invoked to handle an exception.

Such methods may be defined locally within an @Controller or may apply to many @Controller

classes when defined within an @ControllerAdvice class. The following sections explain this in more

detail.

@ExceptionHandler

The HandlerExceptionResolver interface and the SimpleMappingExceptionResolver

implementations allow you to map Exceptions to specific views declaratively along with some optional

Java logic before forwarding to those views. However, in some cases, especially when relying on

@ResponseBody methods rather than on view resolution, it may be more convenient to directly set the

status of the response and optionally write error content to the body of the response.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 489

You can do that with @ExceptionHandler methods. When declared within a controller such methods

apply to exceptions raised by @RequestMapping methods of that contoroller (or any of its sub-classes).

You can also declare an @ExceptionHandler method within an @ControllerAdvice class in

which case it handles exceptions from @RequestMapping methods from many controllers. Below is

an example of a controller-local @ExceptionHandler method:

@Controller

public class SimpleController {

// @RequestMapping methods omitted ...

@ExceptionHandler(IOException.class)

public ResponseEntity<String> handleIOException(IOException ex) {

// prepare responseEntity

return responseEntity;

}

The @ExceptionHandler value can be set to an array of Exception types. If an exception is thrown that

matches one of the types in the list, then the method annotated with the matching @ExceptionHandler

will be invoked. If the annotation value is not set then the exception types listed as method arguments

are used.

Much like standard controller methods annotated with a @RequestMapping annotation, the method

arguments and return values of @ExceptionHandler methods can be flexible. For example, the

HttpServletRequest can be accessed in Servlet environments and the PortletRequest in Portlet

environments. The return type can be a String, which is interpreted as a view name, a ModelAndView

object, a ResponseEntity, or you can also add the @ResponseBody to have the method return value

converted with message converters and written to the response stream.

Handling Standard Spring MVC Exceptions

Spring MVC may raise a number of exceptions while processing a request. The

SimpleMappingExceptionResolver can easily map any exception to a default error view as

needed. However, when working with clients that interpret responses in an automated way you will want

to set specific status code on the response. Depending on the exception raised the status code may

indicate a client error (4xx) or a server error (5xx).

The DefaultHandlerExceptionResolver translates Spring MVC exceptions to specific error

status codes. It is registered by default with the MVC namespace, the MVC Java config, and also by

the the DispatcherServlet (i.e. when not using the MVC namespace or Java config). Listed below

are some of the exceptions handled by this resolver and the corresponding status codes:

Exception HTTP Status Code

BindException 400 (Bad Request)

ConversionNotSupportedException 500 (Internal Server Error)

HttpMediaTypeNotAcceptableException 406 (Not Acceptable)

HttpMediaTypeNotSupportedException 415 (Unsupported Media Type)

HttpMessageNotReadableException 400 (Bad Request)

HttpMessageNotWritableException 500 (Internal Server Error)

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 490

Exception HTTP Status Code

HttpRequestMethodNotSupportedException405 (Method Not Allowed)

MethodArgumentNotValidException 400 (Bad Request)

MissingServletRequestParameterException400 (Bad Request)

MissingServletRequestPartException 400 (Bad Request)

NoHandlerFoundException 404 (Not Found)

NoSuchRequestHandlingMethodException 404 (Not Found)

TypeMismatchException 400 (Bad Request)

The DefaultHandlerExceptionResolver works transparently by setting the status of the

response. However, it stops short of writing any error content to the body of the response

while your application may need to add developer-friendly content to every error response for

example when providing a REST API. You can prepare a ModelAndView and render error

content through view resolution — i.e. by configuring a ContentNegotiatingViewResolver,

MappingJackson2JsonView, and so on. However, you may prefer to use @ExceptionHandler

methods instead.

If you prefer to write error content via @ExceptionHandler methods you can extend

ResponseEntityExceptionHandler instead. This is a convenient base for @ControllerAdvice

classes providing an @ExceptionHandler method to handle standard Spring MVC exceptions and

return ResponseEntity. That allows you to customize the response and write error content with

message converters. See the ResponseEntityExceptionHandler javadocs for more details.

Annotating Business Exceptions With @ResponseStatus

A business exception can be annotated with @ResponseStatus. When the exception is raised, the

ResponseStatusExceptionResolver handles it by setting the status of the response accordingly.

By default the DispatcherServlet registers the ResponseStatusExceptionResolver and it is

available for use.

Customizing the Default Servlet Container Error Page

When the status of the response is set to an error status code and the body of the response is empty,

Servlet containers commonly render an HTML formatted error page. To customize the default error

page of the container, you can declare an <error-page> element in web.xml. Up until Servlet 3,

that element had to be mapped to a specific status code or exception type. Starting with Servlet 3 an

error page does not need to be mapped, which effectively means the specified location customizes the

default Servlet container error page.

<error-page>

<location>/error</location>

</error-page>

Note that the actual location for the error page can be a JSP page or some other URL within the container

including one handled through an @Controller method:

When writing error information, the status code and the error message set on the

HttpServletResponse can be accessed through request attributes in a controller:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 491

@Controller

public class ErrorController {

@RequestMapping(value="/error", produces="application/json")

@ResponseBody

public Map<String, Object> handle(HttpServletRequest request) {

Map<String, Object> map = new HashMap<String, Object>();

map.put("status", request.getAttribute("javax.servlet.error.status_code"));

map.put("reason", request.getAttribute("javax.servlet.error.message"));

return map;

}

or in a JSP:

<%@ page contentType="application/json" pageEncoding="UTF-8"%>

{

status:<%=request.getAttribute("javax.servlet.error.status_code") %>,

reason:<%=request.getAttribute("javax.servlet.error.message") %>

}

17.12 Web Security

The Spring Security project provides features to protect web applications from malicious exploits. Check

out the reference documentation in the sections on "CSRF protection", "Security Response Headers",

and also "Spring MVC Integration". Note that using Spring Security to secure the application is not

necessarily required for all features. For example CSRF protection can be added simply by adding the

CsrfFilter and CsrfRequestDataValueProcessor to your configuration. See the Spring MVC

Showcase for an example.

Another option is to use a framework dedicated to Web Security. HDIV is one such framework and

integrates with Spring MVC.

17.13 Convention over configuration support

For a lot of projects, sticking to established conventions and having reasonable defaults is just what they

(the projects) need, and Spring Web MVC now has explicit support for convention over configuration.

What this means is that if you establish a set of naming conventions and suchlike, you can substantially

cut down on the amount of configuration that is required to set up handler mappings, view resolvers,

ModelAndView instances, etc. This is a great boon with regards to rapid prototyping, and can also lend

a degree of (always good-to-have) consistency across a codebase should you choose to move forward

with it into production.

Convention-over-configuration support addresses the three core areas of MVC: models, views, and

controllers.

The Controller ControllerClassNameHandlerMapping

The ControllerClassNameHandlerMapping class is a HandlerMapping implementation that

uses a convention to determine the mapping between request URLs and the Controller instances

that are to handle those requests.

Consider the following simple Controller implementation. Take special notice of the name of the

class.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 492

public class ViewShoppingCartController implements Controller {

public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

// the implementation is not hugely important for this example...

}

Here is a snippet from the corresponding Spring Web MVC configuration file:

</bean>

The ControllerClassNameHandlerMapping finds all of the various handler (or Controller)

beans defined in its application context and strips Controller off the name to define its handler

mappings. Thus, ViewShoppingCartController maps to the /viewshoppingcart* request

URL.

Let’s look at some more examples so that the central idea becomes immediately familiar. (Notice all

lowercase in the URLs, in contrast to camel-cased Controller class names.)

•WelcomeController maps to the /welcome* request URL

•HomeController maps to the /home* request URL

•IndexController maps to the /index* request URL

•RegisterController maps to the /register* request URL

In the case of MultiActionController handler classes, the mappings generated are slightly

more complex. The Controller names in the following examples are assumed to be

MultiActionController implementations:

•AdminController maps to the /admin/* request URL

•CatalogController maps to the /catalog/* request URL

If you follow the convention of naming your Controller implementations as xxxController,

the ControllerClassNameHandlerMapping saves you the tedium of defining and maintaining a

potentially looooong SimpleUrlHandlerMapping (or suchlike).

The ControllerClassNameHandlerMapping class extends the AbstractHandlerMapping

base class so you can define HandlerInterceptor instances and everything else just as you would

with many other HandlerMapping implementations.

The Model ModelMap (ModelAndView)

The ModelMap class is essentially a glorified Map that can make adding objects that are to be displayed

in (or on) a View adhere to a common naming convention. Consider the following Controller

implementation; notice that objects are added to the ModelAndView without any associated name

specified.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 493

public class DisplayShoppingCartController implements Controller {

public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

List cartItems = // get a List of CartItem objects

User user = // get the User doing the shopping

ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name

mav.addObject(cartItems); <-- look ma, no name, just the object

mav.addObject(user); <-- and again ma!

return mav;

}

The ModelAndView class uses a ModelMap class that is a custom Map implementation that

automatically generates a key for an object when an object is added to it. The strategy for determining

the name for an added object is, in the case of a scalar object such as User, to use the short class

name of the object’s class. The following examples are names that are generated for scalar objects put

into a ModelMap instance.

• An x.y.User instance added will have the name user generated.

• An x.y.Registration instance added will have the name registration generated.

• An x.y.Foo instance added will have the name foo generated.

• A java.util.HashMap instance added will have the name hashMap generated. You probably want

to be explicit about the name in this case because hashMap is less than intuitive.

• Adding null will result in an IllegalArgumentException being thrown. If the object (or objects)

that you are adding could be null, then you will also want to be explicit about the name.

What, no automatic pluralization?

Spring Web MVC’s convention-over-configuration support does not support automatic

pluralization. That is, you cannot add a List of Person objects to a ModelAndView and have

the generated name be people.

This decision was made after some debate, with the "Principle of Least Surprise" winning out in

the end.

The strategy for generating a name after adding a Set or a List is to peek into the collection, take the

short class name of the first object in the collection, and use that with List appended to the name. The

same applies to arrays although with arrays it is not necessary to peek into the array contents. A few

examples will make the semantics of name generation for collections clearer:

• An x.y.User[] array with zero or more x.y.User elements added will have the name userList

generated.

• An x.y.Foo[] array with zero or more x.y.User elements added will have the name fooList

generated.

• A java.util.ArrayList with one or more x.y.User elements added will have the name

userList generated.

• A java.util.HashSet with one or more x.y.Foo elements added will have the name fooList

generated.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 494

• An empty java.util.ArrayList will not be added at all (in effect, the addObject(..) call will

essentially be a no-op).

The View - RequestToViewNameTranslator

The RequestToViewNameTranslator interface determines a logical View name when

no such logical view name is explicitly supplied. It has just one implementation, the

DefaultRequestToViewNameTranslator class.

The DefaultRequestToViewNameTranslator maps request URLs to logical view names, as with

this example:

public class RegistrationController implements Controller {

public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

// process the request...

ModelAndView mav = new ModelAndView();

// add data as necessary to the model...

return mav;

// notice that no View or logical view name has been set

}

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="viewNameTranslator"

class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/>

</bean>

</bean>

</beans>

Notice how in the implementation of the handleRequest(..) method no View or logical view name

is ever set on the ModelAndView that is returned. The DefaultRequestToViewNameTranslator

is tasked with generating a logical view name from the URL of the request. In

the case of the above RegistrationController, which is used in conjunction with

the ControllerClassNameHandlerMapping, a request URL of http://localhost/

registration.html results in a logical view name of registration being generated by the

DefaultRequestToViewNameTranslator. This logical view name is then resolved into the /WEB-

INF/jsp/registration.jsp view by the InternalResourceViewResolver bean.

Tip

You do not need to define a DefaultRequestToViewNameTranslator bean explicitly. If you

like the default settings of the DefaultRequestToViewNameTranslator, you can rely on the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 495

Spring Web MVC DispatcherServlet to instantiate an instance of this class if one is not

explicitly configured.

Of course, if you need to change the default settings, then you do need to configure

your own DefaultRequestToViewNameTranslator bean explicitly. Consult the comprehensive

DefaultRequestToViewNameTranslator javadocs for details on the various properties that can

be configured.

17.14 ETag support

An ETag (entity tag) is an HTTP response header returned by an HTTP/1.1 compliant web server used to

determine change in content at a given URL. It can be considered to be the more sophisticated successor

to the Last-Modified header. When a server returns a representation with an ETag header, the

client can use this header in subsequent GETs, in an If-None-Match header. If the content has not

changed, the server returns 304: Not Modified.

Support for ETags is provided by the Servlet filter ShallowEtagHeaderFilter. It is a

plain Servlet Filter, and thus can be used in combination with any web framework. The

ShallowEtagHeaderFilter filter creates so-called shallow ETags (as opposed to deep ETags, more

about that later).The filter caches the content of the rendered JSP (or other content), generates an MD5

hash over that, and returns that as an ETag header in the response. The next time a client sends a

request for the same resource, it uses that hash as the If-None-Match value. The filter detects this,

renders the view again, and compares the two hashes. If they are equal, a 304 is returned. This filter

will not save processing power, as the view is still rendered. The only thing it saves is bandwidth, as

the rendered response is not sent back over the wire.

You configure the ShallowEtagHeaderFilter in web.xml:

<filter-name>etagFilter</filter-name>

<filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>etagFilter</filter-name>

<servlet-name>petclinic</servlet-name>

</filter-mapping>

17.15 Code-based Servlet container initialization

In a Servlet 3.0+ environment, you have the option of configuring the Servlet container programmatically

as an alternative or in combination with a web.xml file. Below is an example of registering a

DispatcherServlet:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 496

import org.springframework.web.WebApplicationInitializer;

public class MyWebApplicationInitializer implements WebApplicationInitializer {

@Override

public void onStartup(ServletContext container) {

XmlWebApplicationContext appContext = new XmlWebApplicationContext();

appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");

ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new

DispatcherServlet(appContext));

registration.setLoadOnStartup(1);

registration.addMapping("/");

}

WebApplicationInitializer is an interface provided by Spring MVC that ensures

your implementation is detected and automatically used to initialize any Servlet 3

container. An abstract base class implementation of WebApplicationInitializer

named AbstractDispatcherServletInitializer makes it even easier to register the

DispatcherServlet by simply overriding methods to specify the servlet mapping and the location of

the DispatcherServlet configuration:

public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

@Override

protected Class<?>[] getRootConfigClasses() {

return null;

}

@Override

protected Class<?>[] getServletConfigClasses() {

return new Class[] { MyWebConfig.class };

}

@Override

protected String[] getServletMappings() {

return new String[] { "/" };

}

The above example is for an application that uses Java-based Spring configuration. If using XML-based

Spring configuration, extend directly from AbstractDispatcherServletInitializer:

public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

@Override

protected WebApplicationContext createRootApplicationContext() {

return null;

}

@Override

protected WebApplicationContext createServletApplicationContext() {

XmlWebApplicationContext cxt = new XmlWebApplicationContext();

cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");

return cxt;

}

@Override

protected String[] getServletMappings() {

return new String[] { "/" };

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 497

AbstractDispatcherServletInitializer also provides a convenient way to add Filter

instances and have them automatically mapped to the DispatcherServlet:

public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

// ...

@Override

protected Filter[] getServletFilters() {

return new Filter[] { new HiddenHttpMethodFilter(), new CharacterEncodingFilter() };

}

Each filter is added with a default name based on its concrete type and automatically mapped to the

DispatcherServlet.

The isAsyncSupported protected method of AbstractDispatcherServletInitializer

provides a single place to enable async support on the DispatcherServlet and all filters mapped

to it. By default this flag is set to true.

17.16 Configuring Spring MVC

the section called “Special Bean Types In the WebApplicationContext” and the section called

“Default DispatcherServlet Configuration” explained about Spring MVC’s special beans and the default

implementations used by the DispatcherServlet. In this section you’ll learn about two additional

ways of configuring Spring MVC. Namely the MVC Java config and the MVC XML namespace.

The MVC Java config and the MVC namespace provide similar default configuration that overrides the

DispatcherServlet defaults. The goal is to spare most applications from having to having to create

the same configuration and also to provide higher-level constructs for configuring Spring MVC that serve

as a simple starting point and require little or no prior knowledge of the underlying configuration.

You can choose either the MVC Java config or the MVC namespace depending on your preference. Also

as you will see further below, with the MVC Java config it is easier to see the underlying configuration

as well as to make fine-grained customizations directly to the created Spring MVC beans. But let’s start

from the beginning.

Enabling the MVC Java Config or the MVC XML Namespace

To enable MVC Java config add the annotation @EnableWebMvc to one of your @Configuration

classes:

@Configuration

@EnableWebMvc

public class WebConfig {

}

To achieve the same in XML use the mvc:annotation-driven element in your DispatcherServlet

context (or in your root context if you have no DispatcherServlet context defined):

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 498

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:mvc="http://www.springframework.org/schema/mvc"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/mvc

http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<mvc:annotation-driven />

</beans>

The above registers a RequestMappingHandlerMapping, a RequestMappingHandlerAdapter,

and an ExceptionHandlerExceptionResolver (among others) in support of processing

requests with annotated controller methods using annotations such as @RequestMapping,

@ExceptionHandler, and others.

It also enables the following:

1. Spring 3 style type conversion through a ConversionService instance in addition to the JavaBeans

PropertyEditors used for Data Binding.

2. Support for formatting Number fields using the @NumberFormat annotation through the

ConversionService.

3. Support for formatting Date, Calendar, Long, and Joda Time fields using the @DateTimeFormat

annotation.

4. Support for validating @Controller inputs with @Valid, if a JSR-303 Provider is present on the

classpath.

5. HttpMessageConverter support for @RequestBody method parameters and @ResponseBody

method return values from @RequestMapping or @ExceptionHandler methods.

This is the complete list of HttpMessageConverters set up by mvc:annotation-driven:

a. ByteArrayHttpMessageConverter converts byte arrays.

b. StringHttpMessageConverter converts strings.

c. ResourceHttpMessageConverter converts to/from

org.springframework.core.io.Resource for all media types.

d. SourceHttpMessageConverter converts to/from a javax.xml.transform.Source.

e. FormHttpMessageConverter converts form data to/from a MultiValueMap<String,

String>.

f. Jaxb2RootElementHttpMessageConverter converts Java objects to/from XML — added if

JAXB2 is present and Jackson 2 XML extension is not present on the classpath.

g. MappingJackson2HttpMessageConverter converts to/from JSON — added if Jackson 2 is

present on the classpath.

h. MappingJackson2XmlHttpMessageConverter converts to/from XML — added if Jackson 2

XML extension is present on the classpath.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 499

i. AtomFeedHttpMessageConverter converts Atom feeds — added if Rome is present on the

classpath.

j. RssChannelHttpMessageConverter converts RSS feeds — added if Rome is present on the

classpath.

Customizing the Provided Configuration

To customize the default configuration in Java you simply implement the WebMvcConfigurer interface

or more likely extend the class WebMvcConfigurerAdapter and override the methods you need.

Below is an example of some of the available methods to override. See WebMvcConfigurer for a list

of all methods and the javadocs for further details:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

protected void addFormatters(FormatterRegistry registry) {

// Add formatters and/or converters

}

@Override

public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {

// Configure the list of HttpMessageConverters to use

}

To customize the default configuration of <mvc:annotation-driven /> check what attributes and

sub-elements it supports. You can view the Spring MVC XML schema or use the code completion feature

of your IDE to discover what attributes and sub-elements are available. The sample below shows a

subset of what is available:

<mvc:annotation-driven conversion-service="conversionService">

<mvc:message-converters>

</mvc:message-converters>

</mvc:annotation-driven>

<list>

</list>

</property>

</bean>

Interceptors

You can configure HandlerInterceptors or WebRequestInterceptors to be applied to all

incoming requests or restricted to specific URL path patterns.

An example of registering interceptors in Java:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 500

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addInterceptors(InterceptorRegistry registry) {

registry.addInterceptor(new LocaleInterceptor());

registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/").excludePathPatterns("/

admin/");

registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");

}

And in XML use the <mvc:interceptors> element:

<mvc:interceptors>

<mvc:interceptor>

<mvc:mapping path="/"/>

<mvc:exclude-mapping path="/admin/"/>

</mvc:interceptor>

<mvc:interceptor>

<mvc:mapping path="/secure/*"/>

</mvc:interceptor>

</mvc:interceptors>

Content Negotiation

You can configure how Spring MVC determines the requested media types from the client for request

mapping as well as for content negotiation purposes. The available options are to check the file extension

in the request URI, the "Accept" header, a request parameter, as well as to fall back on a default content

type. By default, file extension in the request URI is checked first and the "Accept" header is checked

next.

For file extensions in the request URI, the MVC Java config and the MVC namespace, automatically

as Jackson, JAXB2, or Rome are present on the classpath. Additional extensions may be not need to be

registered explicitly if they can be discovered via ServletContext.getMimeType(String) or the

Java Activation Framework (see javax.activation.MimetypesFileTypeMap). You can register

more extensions with the setUseRegisteredSuffixPatternMatch method.

The introduction of ContentNegotiationManager also enables selective suffix pattern matching for

incoming requests. For more details, see its javadocs.

Below is an example of customizing content negotiation options through the MVC Java config:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {

configurer.favorPathExtension(false).favorParameter(true);

}

In the MVC namespace, the <mvc:annotation-driven> element has a content-negotiation-

manager attribute, which expects a ContentNegotiationManager that in turn can be created with

a ContentNegotiationManagerFactoryBean:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 501

<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" />

<value>

json=application/json

xml=application/xml

</value>

</property>

</bean>

If not using the MVC Java config or the MVC namespace, you’ll

need to create an instance of ContentNegotiationManager and use it

to configure RequestMappingHandlerMapping for request mapping purposes, and

RequestMappingHandlerAdapter and ExceptionHandlerExceptionResolver for content

negotiation purposes.

Note that ContentNegotiatingViewResolver now can also be configured with a

ContentNegotiatingViewResolver, so you can use one instance throughout Spring MVC.

In more advanced cases, it may be useful to configure multiple ContentNegotiationManager

instances that in turn may contain custom ContentNegotiationStrategy implementations.

For example you could configure ExceptionHandlerExceptionResolver with a

ContentNegotiationManager that always resolves the requested media type to "application/

json". Or you may want to plug a custom strategy that has some logic to select a default content type

(e.g. either XML or JSON) if no content types were requested.

View Controllers

This is a shortcut for defining a ParameterizableViewController that immediately forwards to a

view when invoked. Use it in static cases when there is no Java controller logic to execute before the

view generates the response.

An example of forwarding a request for "/" to a view called "home" in Java:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addViewControllers(ViewControllerRegistry registry) {

registry.addViewController("/").setViewName("home");

}

And the same in XML use the <mvc:view-controller> element:

<mvc:view-controller path="/" view-name="home"/>

View Resolvers

The MVC config simplifies the registration of view resolvers.

The following is a Java config example that configures content negotiation view resolution using

FreeMarker HTML templates and Jackson as a default View for JSON rendering:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 502

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configureViewResolvers(ViewResolverRegistry registry) {

registry.enableContentNegotiation(new MappingJackson2JsonView());

registry.jsp();

}

And the same in XML:

<mvc:view-resolvers>

<mvc:content-negotiation>

<mvc:default-views>

</mvc:default-views>

</mvc:content-negotiation>

<mvc:jsp />

</mvc:view-resolvers>

Note however that FreeMarker, Velocity, Tiles, and Groovy Markup also require configuration of the

underlying view technology.

The MVC namespace provides dedicated elements. For example with FreeMarker:

<mvc:view-resolvers>

<mvc:content-negotiation>

<mvc:default-views>

</mvc:default-views>

</mvc:content-negotiation>

<mvc:freemarker cache="false" />

</mvc:view-resolvers>

<mvc:freemarker-configurer>

<mvc:template-loader-path location="/freemarker" />

</mvc:freemarker-configurer>

In Java config simply add the respective "Configurer" bean:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configureViewResolvers(ViewResolverRegistry registry) {

registry.enableContentNegotiation(new MappingJackson2JsonView());

registry.freeMarker().cache(false);

}

@Bean

public FreeMarkerConfigurer freeMarkerConfigurer() {

FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();

configurer.setTemplateLoaderPath("/WEB-INF/");

return configurer;

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 503

Serving of Resources

This option allows static resource requests following a particular URL pattern to be served by a

ResourceHttpRequestHandler from any of a list of Resource locations. This provides a convenient

way to serve static resources from locations other than the web application root, including locations on

the classpath. The cache-period property may be used to set far future expiration headers (1 year

is the recommendation of optimization tools such as Page Speed and YSlow) so that they will be more

efficiently utilized by the client. The handler also properly evaluates the Last-Modified header (if

present) so that a 304 status code will be returned as appropriate, avoiding unnecessary overhead for

resources that are already cached by the client. For example, to serve resource requests with a URL

pattern of /resources/** from a public-resources directory within the web application root you

would use:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addResourceHandlers(ResourceHandlerRegistry registry) {

registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/");

}

And the same in XML:

<mvc:resources mapping="/resources/**" location="/public-resources/"/>

To serve these resources with a 1-year future expiration to ensure maximum use of the browser cache

and a reduction in HTTP requests made by the browser:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addResourceHandlers(ResourceHandlerRegistry registry) {

registry.addResourceHandler("/resources/**").addResourceLocations("/public-

resources/").setCachePeriod(31556926);

}

And in XML:

<mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/>

The mapping attribute must be an Ant pattern that can be used by SimpleUrlHandlerMapping, and

the location attribute must specify one or more valid resource directory locations. Multiple resource

locations may be specified using a comma-separated list of values. The locations specified will be

checked in the specified order for the presence of the resource for any given request. For example, to

enable the serving of resources from both the web application root and from a known path of /META-

INF/public-web-resources/ in any jar on the classpath use:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 504

@EnableWebMvc

@Configuration

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addResourceHandlers(ResourceHandlerRegistry registry) {

registry.addResourceHandler("/resources/**")

.addResourceLocations("/", "classpath:/META-INF/public-web-resources/");

}

And in XML:

<mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/>

When serving resources that may change when a new version of the application is deployed it is

recommended that you incorporate a version string into the mapping pattern used to request the

resources so that you may force clients to request the newly deployed version of your application’s

resources. Support for versioned URLs is built into the framework and can be enabled by configuring a

resource chain on the resource handler. The chain consists of one more ResourceResolver instances

followed by one or more ResourceTransformer instances. Together they can provide arbitrary

resolution and transformation of resources.

The built-in VersionResourceResolver can be configured with different strategies. For

example a FixedVersionStrategy can use a property, a date, or other as the version. A

ContentVersionStrategy uses an MD5 hash computed from the content of the resource (known

as "fingerprinting" URLs).

ContentVersionStrategy is a good default choice to use except in cases where it cannot be used

(e.g. with JavaScript module loaders). You can configure different version strategies against different

patterns as shown below. Keep in mind also that computing content-based versions is expensive and

therefore resource chain caching should be enabled in production.

Java config example;

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void addResourceHandlers(ResourceHandlerRegistry registry) {

registry.addResourceHandler("/resources/")

.addResourceLocations("/public-resources/")

.resourceChain(true).addResolver(

new VersionResourceResolver().addContentVersionStrategy("/"));

}

XML example:

<mvc:resources mapping="/resources/" location="/public-resources/">

<mvc:resource-chain>

<mvc:resource-cache />

<mvc:resolvers>

<mvc:version-resolver>

<mvc:content-version-strategy patterns="/"/>

</mvc:version-resolver>

</mvc:resolvers>

</mvc:resource-chain>

</mvc:resources>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 505

In order for the above to work the application must also render URLs with versions. The easiest way to

do that is to configure the ResourceUrlEncodingFilter which wraps the response and overrides

its encodeURL method. This will work in JSPs, FreeMarker, Velocity, and any other view technology

that calls the response encodeURL method. Alternatively, an application can also inject and use directly

the ResourceUrlProvider bean, which is automatically declared with the MVC Java config and the

MVC namespace.

Falling Back On the "Default" Servlet To Serve Resources

This allows for mapping the DispatcherServlet to "/" (thus overriding the mapping of the container’s

default Servlet), while still allowing static resource requests to be handled by the container’s default

Servlet. It configures a DefaultServletHttpRequestHandler with a URL mapping of "/**" and the

lowest priority relative to other URL mappings.

This handler will forward all requests to the default Servlet. Therefore it is important that it remains last

in the order of all other URL HandlerMappings. That will be the case if you use <mvc:annotation-

driven> or alternatively if you are setting up your own customized HandlerMapping instance be sure

to set its order property to a value lower than that of the DefaultServletHttpRequestHandler,

which is Integer.MAX_VALUE.

To enable the feature using the default setup use:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {

configurer.enable();

}

Or in XML:

<mvc:default-servlet-handler/>

The caveat to overriding the "/" Servlet mapping is that the RequestDispatcher for the default Servlet

must be retrieved by name rather than by path. The DefaultServletHttpRequestHandler will

attempt to auto-detect the default Servlet for the container at startup time, using a list of known names

for most of the major Servlet containers (including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic,

and WebSphere). If the default Servlet has been custom configured with a different name, or if a different

Servlet container is being used where the default Servlet name is unknown, then the default Servlet’s

name must be explicitly provided as in the following example:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {

configurer.enable("myCustomDefaultServlet");

}

Or in XML:

<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 506

Path Matching

This allows customizing various settings related to URL mapping and path matching. For details on the

individual options check out the PathMatchConfigurer API.

Below is an example in Java config:

@Configuration

@EnableWebMvc

public class WebConfig extends WebMvcConfigurerAdapter {

@Override

public void configurePathMatch(PathMatchConfigurer configurer) {

configurer

.setUseSuffixPatternMatch(true)

.setUseTrailingSlashMatch(false)

.setUseRegisteredSuffixPatternMatch(true)

.setPathMatcher(antPathMatcher())

.setUrlPathHelper(urlPathHelper());

}

@Bean

public UrlPathHelper urlPathHelper() {

//...

}

@Bean

public PathMatcher antPathMatcher() {

//...

}

And the same in XML, use the <mvc:path-matching> element:

<mvc:annotation-driven>

<mvc:path-matching

suffix-pattern="true"

trailing-slash="false"

registered-suffixes-only="true"

path-helper="pathHelper"

path-matcher="pathMatcher" />

</mvc:annotation-driven>

Advanced Customizations with MVC Java Config

As you can see from the above examples, MVC Java config and the MVC namespace provide higher

level constructs that do not require deep knowledge of the underlying beans created for you. Instead it

helps you to focus on your application needs. However, at some point you may need more fine-grained

control or you may simply wish to understand the underlying configuration.

The first step towards more fine-grained control is to see the underlying beans created for you. In MVC

Java config you can see the javadocs and the @Bean methods in WebMvcConfigurationSupport.

The configuration in this class is automatically imported through the @EnableWebMvc annotation. In

fact if you open @EnableWebMvc you can see the @Import statement.

The next step towards more fine-grained control is to customize a property on one of the beans

created in WebMvcConfigurationSupport or perhaps to provide your own instance. This requires

two things — remove the @EnableWebMvc annotation in order to prevent the import and then extend

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 507

from DelegatingWebMvcConfiguration, a subclass of WebMvcConfigurationSupport. Here

is an example:

@Configuration

public class WebConfig extends DelegatingWebMvcConfiguration {

@Override

public void addInterceptors(InterceptorRegistry registry){

// ...

}

@Override

@Bean

public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {

// Create or let "super" create the adapter

// Then customize one of its properties

}

Note

An application should have only one configuration extending

DelegatingWebMvcConfiguration or a single @EnableWebMvc annotated class, since they

both register the same underlying beans.

Modifying beans in this way does not prevent you from using any of the higher-level

constructs shown earlier in this section. WebMvcConfigurerAdapter subclasses and

WebMvcConfigurer implementations are still being used.

Advanced Customizations with the MVC Namespace

Fine-grained control over the configuration created for you is a bit harder with the MVC namespace.

If you do need to do that, rather than replicating the configuration it provides, consider configuring a

BeanPostProcessor that detects the bean you want to customize by type and then modifying its

properties as necessary. For example:

@Component

public class MyPostProcessor implements BeanPostProcessor {

public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {

if (bean instanceof RequestMappingHandlerAdapter) {

// Modify properties of the adapter

}

Note that MyPostProcessor needs to be included in an <component scan /> in order for it to be

detected or if you prefer you can declare it explicitly with an XML bean declaration.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 508

18. View technologies

18.1 Introduction

One of the areas in which Spring excels is in the separation of view technologies from the rest of the MVC

framework. For example, deciding to use Velocity or XSLT in place of an existing JSP is primarily a matter

of configuration. This chapter covers the major view technologies that work with Spring and touches

briefly on how to add new ones. This chapter assumes you are already familiar with Section 17.5,

“Resolving views” which covers the basics of how views in general are coupled to the MVC framework.

18.2 JSP & JSTL

Spring provides a couple of out-of-the-box solutions for JSP and JSTL views. Using JSP or JSTL is

done using a normal view resolver defined in the WebApplicationContext. Furthermore, of course

you need to write some JSPs that will actually render the view.

Note

Setting up your application to use JSTL is a common source of error, mainly caused by confusion

over the different servlet spec., JSP and JSTL version numbers, what they mean and how to

declare the taglibs correctly. The article How to Reference and Use JSTL in your Web Application

provides a useful guide to the common pitfalls and how to avoid them. Note that as of Spring 3.0,

the minimum supported servlet version is 2.4 (JSP 2.0 and JSTL 1.1), which reduces the scope

for confusion somewhat.

View resolvers

Just as with any other view technology you’re integrating with Spring, for JSPs you’ll need a view resolver

that will resolve your views. The most commonly used view resolvers when developing with JSPs are the

InternalResourceViewResolver and the ResourceBundleViewResolver. Both are declared

in the WebApplicationContext:

</bean>

# And a sample properties file is uses (views.properties in WEB-INF/classes):

welcome.(class)=org.springframework.web.servlet.view.JstlView

welcome.url=/WEB-INF/jsp/welcome.jsp

productList.(class)=org.springframework.web.servlet.view.JstlView

productList.url=/WEB-INF/jsp/productlist.jsp

As you can see, the ResourceBundleViewResolver needs a properties file defining the view names

mapped to 1) a class and 2) a URL. With a ResourceBundleViewResolver you can mix different

types of views using only one resolver.

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 509

The InternalResourceBundleViewResolver can be configured for using JSPs as described

above. As a best practice, we strongly encourage placing your JSP files in a directory under the 'WEB-

INF' directory, so there can be no direct access by clients.

Plain-old JSPs versus JSTL

When using the Java Standard Tag Library you must use a special view class, the JstlView, as JSTL

needs some preparation before things such as the I18N features will work.

Additional tags facilitating development

Spring provides data binding of request parameters to command objects as described in earlier chapters.

To facilitate the development of JSP pages in combination with those data binding features, Spring

provides a few tags that make things even easier. All Spring tags haveHTML escaping features to enable

or disable escaping of characters.

The tag library descriptor (TLD) is included in the spring-webmvc.jar. Further information about the

individual tags can be found in the appendix entitled Chapter 36, spring.tld.

Using Spring’s form tag library

As of version 2.0, Spring provides a comprehensive set of data binding-aware tags for handling form

elements when using JSP and Spring Web MVC. Each tag provides support for the set of attributes of its

corresponding HTML tag counterpart, making the tags familiar and intuitive to use. The tag-generated

HTML is HTML 4.01/XHTML 1.0 compliant.

Unlike other form/input tag libraries, Spring’s form tag library is integrated with Spring Web MVC, giving

the tags access to the command object and reference data your controller deals with. As you will see

in the following examples, the form tags make JSPs easier to develop, read and maintain.

Let’s go through the form tags and look at an example of how each tag is used. We have included

generated HTML snippets where certain tags require further commentary.

Configuration

The form tag library comes bundled in spring-webmvc.jar. The library descriptor is called spring-

form.tld.

To use the tags from this library, add the following directive to the top of your JSP page:

<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>

where form is the tag name prefix you want to use for the tags from this library.

The form tag

This tag renders an HTML form tag and exposes a binding path to inner tags for binding. It puts the

command object in the PageContext so that the command object can be accessed by inner tags. All

the other tags in this library are nested tags of the form tag.

Let’s assume we have a domain object called User. It is a JavaBean with properties such as firstName

and lastName. We will use it as the form backing object of our form controller which returns form.jsp.

Below is an example of what form.jsp would look like:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 510

<form:form>

<table>

<tr>

<td>First Name:</td>

</tr>

<tr>

</tr>

<tr>

</td>

</tr>

</table>

</form:form>

The firstName and lastName values are retrieved from the command object placed in the

PageContext by the page controller. Keep reading to see more complex examples of how inner tags

are used with the form tag.

The generated HTML looks like a standard form:

<table>

<tr>

<td>First Name:</td>

</tr>

<tr>

</tr>

<tr>

</td>

</tr>

</table>

</form>

The preceding JSP assumes that the variable name of the form backing object is 'command'. If you

have put the form backing object into the model under another name (definitely a best practice), then

you can bind the form to the named variable like so:

<form:form commandName="user">

<table>

<tr>

<td>First Name:</td>

</tr>

<tr>

</tr>

<tr>

</td>

</tr>

</table>

</form:form>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 511

The input tag

This tag renders an HTML input tag using the bound value and type=text by default. For an example of

this tag, see the section called “The form tag”. Starting with Spring 3.1 you can use other types such

HTML5-specific types like email, tel, date, and others.

The checkbox tag

This tag renders an HTML input tag with type checkbox.

Let’s assume our User has preferences such as newsletter subscription and a list of hobbies. Below

is an example of the Preferences class:

public class Preferences {

private boolean receiveNewsletter;

private String[] interests;

private String favouriteWord;

public boolean isReceiveNewsletter() {

return receiveNewsletter;

}

public void setReceiveNewsletter(boolean receiveNewsletter) {

this.receiveNewsletter = receiveNewsletter;

}

public String[] getInterests() {

return interests;

}

public void setInterests(String[] interests) {

this.interests = interests;

}

public String getFavouriteWord() {

return favouriteWord;

}

public void setFavouriteWord(String favouriteWord) {

this.favouriteWord = favouriteWord;

}

The form.jsp would look like:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 512

<form:form>

<table>

<tr>

<td>Subscribe to newsletter?:</td>

<%-- Approach 1: Property is of type java.lang.Boolean --%>

</tr>

<tr>

<td>Interests:</td>

<%-- Approach 2: Property is of an array or of type java.util.Collection --%>

<td>

Quidditch: <form:checkbox path="preferences.interests" value="Quidditch"/>

Herbology: <form:checkbox path="preferences.interests" value="Herbology"/>

Defence Against the Dark

Arts: <form:checkbox path="preferences.interests" value="Defence Against the Dark Arts"/>

</td>

</tr>

<tr>

<td>Favourite Word:</td>

<%-- Approach 3: Property is of type java.lang.Object --%>

<td>

Magic: <form:checkbox path="preferences.favouriteWord" value="Magic"/>

</td>

</tr>

</table>

</form:form>

There are 3 approaches to the checkbox tag which should meet all your checkbox needs.

• Approach One - When the bound value is of type java.lang.Boolean, the input(checkbox)

is marked as checked if the bound value is true. The value attribute corresponds to the resolved

value of the setValue(Object) value property.

• Approach Two - When the bound value is of type array or java.util.Collection, the

input(checkbox) is marked as checked if the configured setValue(Object) value is present

in the bound Collection.

• Approach Three - For any other bound value type, the input(checkbox) is marked as checked if

the configured setValue(Object) is equal to the bound value.

Note that regardless of the approach, the same HTML structure is generated. Below is an HTML snippet

of some checkboxes:

<tr>

<td>Interests:</td>

<td>

Quidditch: <input name="preferences.interests" type="checkbox" value="Quidditch"/>

Herbology: <input name="preferences.interests" type="checkbox" value="Herbology"/>

Defence Against the Dark

Arts: <input name="preferences.interests" type="checkbox" value="Defence Against the Dark Arts"/>

</td>

</tr>

What you might not expect to see is the additional hidden field after each checkbox. When a checkbox

in an HTML page is not checked, its value will not be sent to the server as part of the HTTP request

parameters once the form is submitted, so we need a workaround for this quirk in HTML in order for

Spring form data binding to work. The checkbox tag follows the existing Spring convention of including

a hidden parameter prefixed by an underscore ("_") for each checkbox. By doing this, you are effectively

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 513

telling Spring that "the checkbox was visible in the form and I want my object to which the form data will

be bound to reflect the state of the checkbox no matter what".

The checkboxes tag

This tag renders multiple HTML input tags with type checkbox.

Building on the example from the previous checkbox tag section. Sometimes you prefer not to have to

list all the possible hobbies in your JSP page. You would rather provide a list at runtime of the available

options and pass that in to the tag. That is the purpose of the checkboxes tag. You pass in an Array,

a List or a Map containing the available options in the "items" property. Typically the bound property

is a collection so it can hold multiple values selected by the user. Below is an example of the JSP using

this tag:

<form:form>

<table>

<tr>

<td>Interests:</td>

<td>

<%-- Property is of an array or of type java.util.Collection --%>

<form:checkboxes path="preferences.interests" items="${interestList}"/>

</td>

</tr>

</table>

</form:form>

This example assumes that the "interestList" is a List available as a model attribute containing strings

of the values to be selected from. In the case where you use a Map, the map entry key will be used

as the value and the map entry’s value will be used as the label to be displayed. You can also use a

custom object where you can provide the property names for the value using "itemValue" and the label

using "itemLabel".

The radiobutton tag

This tag renders an HTML input tag with type radio.

A typical usage pattern will involve multiple tag instances bound to the same property but with different

values.

<tr>

<td>

Male: <form:radiobutton path="sex" value="M"/> <br/>

Female: <form:radiobutton path="sex" value="F"/>

</td>

</tr>

The radiobuttons tag

This tag renders multiple HTML input tags with type radio.

Just like the checkboxes tag above, you might want to pass in the available options as a runtime

variable. For this usage you would use the radiobuttons tag. You pass in an Array, a List or a Map

containing the available options in the "items" property. In the case where you use a Map, the map entry

key will be used as the value and the map entry’s value will be used as the label to be displayed. You

can also use a custom object where you can provide the property names for the value using "itemValue"

and the label using "itemLabel".

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 514

<tr>

</tr>

The password tag

This tag renders an HTML input tag with type password using the bound value.

<tr>

<td>Password:</td>

<td>

<form:password path="password" />

</td>

</tr>

Please note that by default, the password value is not shown. If you do want the password value to be

shown, then set the value of the 'showPassword' attribute to true, like so.

<tr>

<td>Password:</td>

<td>

<form:password path="password" value="^76525bvHGq" showPassword="true" />

</td>

</tr>

The select tag

This tag renders an HTML select element. It supports data binding to the selected option as well as the

use of nested option and options tags.

Let’s assume a User has a list of skills.

<tr>

<td>Skills:</td>

</tr>

If the User's skill were in Herbology, the HTML source of the Skills row would look like:

<tr>

<td>Skills:</td>

<td>

<option value="Potions">Potions</option>

<option value="Herbology" selected="selected">Herbology</option>

<option value="Quidditch">Quidditch</option>

</select>

</td>

</tr>

The option tag

This tag renders an HTML option. It sets selected as appropriate based on the bound value.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 515

<tr>

<td>House:</td>

<td>

<form:select path="house">

<form:option value="Gryffindor"/>

<form:option value="Hufflepuff"/>

<form:option value="Ravenclaw"/>

<form:option value="Slytherin"/>

</form:select>

</td>

</tr>

If the User's house was in Gryffindor, the HTML source of the House row would look like:

<tr>

<td>House:</td>

<td>

<option value="Gryffindor" selected="selected">Gryffindor</option>

<option value="Hufflepuff">Hufflepuff</option>

<option value="Ravenclaw">Ravenclaw</option>

<option value="Slytherin">Slytherin</option>

</select>

</td>

</tr>

The options tag

This tag renders a list of HTML option tags. It sets the selected attribute as appropriate based on the

bound value.

<tr>

<td>Country:</td>

<td>

<form:select path="country">

<form:option value="-" label="--Please Select"/>

<form:options items="${countryList}" itemValue="code" itemLabel="name"/>

</form:select>

</td>

</tr>

If the User lived in the UK, the HTML source of the Country row would look like:

<tr>

<td>Country:</td>

<td>

<option value="-">--Please Select</option>

<option value="AT">Austria</option>

<option value="UK" selected="selected">United Kingdom</option>

<option value="US">United States</option>

</select>

</td>

</tr>

As the example shows, the combined usage of an option tag with the options tag generates the

same standard HTML, but allows you to explicitly specify a value in the JSP that is for display only

(where it belongs) such as the default string in the example: "-- Please Select".

The items attribute is typically populated with a collection or array of item objects. itemValue and

itemLabel simply refer to bean properties of those item objects, if specified; otherwise, the item objects

themselves will be stringified. Alternatively, you may specify a Map of items, in which case the map keys

are interpreted as option values and the map values correspond to option labels. If itemValue and/or

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 516

itemLabel happen to be specified as well, the item value property will apply to the map key and the

item label property will apply to the map value.

The textarea tag

This tag renders an HTML textarea.

<tr>

<td>Notes:</td>

</tr>

The hidden tag

This tag renders an HTML input tag with type hidden using the bound value. To submit an unbound

hidden value, use the HTML input tag with type hidden.

<form:hidden path="house" />

If we choose to submit the house value as a hidden one, the HTML would look like:

The errors tag

This tag renders field errors in an HTML span tag. It provides access to the errors created in your

controller or those that were created by any validators associated with your controller.

Let’s assume we want to display all error messages for the firstName and lastName fields once we

submit the form. We have a validator for instances of the User class called UserValidator.

public class UserValidator implements Validator {

public boolean supports(Class candidate) {

return User.class.isAssignableFrom(candidate);

}

public void validate(Object obj, Errors errors) {

ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "required", "Field is

required.");

ValidationUtils.rejectIfEmptyOrWhitespace(errors, "lastName", "required", "Field is required.");

}

The form.jsp would look like:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 517

<form:form>

<table>

<tr>

<td>First Name:</td>

<%-- Show errors for firstName field --%>

</tr>

<tr>

<%-- Show errors for lastName field --%>

</tr>

<tr>

</td>

</tr>

</table>

</form:form>

If we submit a form with empty values in the firstName and lastName fields, this is what the HTML

would look like:

<table>

<tr>

<td>First Name:</td>

<%-- Associated errors to firstName field displayed --%>

<td><span name="firstName.errors">Field is required.</span></td>

</tr>

<tr>

<%-- Associated errors to lastName field displayed --%>

<td><span name="lastName.errors">Field is required.</span></td>

</tr>

<tr>

</td>

</tr>

</table>

</form>

What if we want to display the entire list of errors for a given page? The example below shows that the

errors tag also supports some basic wildcarding functionality.

•path="*" - displays all errors

•path="lastName" - displays all errors associated with the lastName field

• if path is omitted - object errors only are displayed

The example below will display a list of errors at the top of the page, followed by field-specific errors

next to the fields:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 518

<form:form>

<form:errors path="*" cssClass="errorBox" />

<table>

<tr>

<td>First Name:</td>

</tr>

<tr>

</tr>

<tr>

</td>

</tr>

</table>

</form:form>

The HTML would look like:

<span name="*.errors" class="errorBox">Field is required.<br/>Field is required.</span>

<table>

<tr>

<td>First Name:</td>

<td><span name="firstName.errors">Field is required.</span></td>

</tr>

<tr>

<td><span name="lastName.errors">Field is required.</span></td>

</tr>

<tr>

</td>

</tr>

</form>

HTTP Method Conversion

A key principle of REST is the use of the Uniform Interface. This means that all resources (URLs) can be

manipulated using the same four HTTP methods: GET, PUT, POST, and DELETE. For each method,

the HTTP specification defines the exact semantics. For instance, a GET should always be a safe

operation, meaning that is has no side effects, and a PUT or DELETE should be idempotent, meaning

that you can repeat these operations over and over again, but the end result should be the same. While

HTTP defines these four methods, HTML only supports two: GET and POST. Fortunately, there are

two possible workarounds: you can either use JavaScript to do your PUT or DELETE, or simply do a

POST with the real method as an additional parameter (modeled as a hidden input field in an HTML

form). This latter trick is what Spring’s HiddenHttpMethodFilter does. This filter is a plain Servlet

Filter and therefore it can be used in combination with any web framework (not just Spring MVC). Simply

add this filter to your web.xml, and a POST with a hidden _method parameter will be converted into the

corresponding HTTP method request.

To support HTTP method conversion the Spring MVC form tag was updated to support setting the HTTP

method. For example, the following snippet taken from the updated Petclinic sample

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 519

<form:form method="delete">

</form:form>

This will actually perform an HTTP POST, with the real DELETE method hidden behind a request

parameter, to be picked up by the HiddenHttpMethodFilter, as defined in web.xml:

<filter-name>httpMethodFilter</filter-name>

<filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>httpMethodFilter</filter-name>

<servlet-name>petclinic</servlet-name>

</filter-mapping>

The corresponding @Controller method is shown below:

@RequestMapping(method = RequestMethod.DELETE)

public String deletePet(@PathVariable int ownerId, @PathVariable int petId) {

this.clinic.deletePet(petId);

return "redirect:/owners/" + ownerId;

}

HTML5 Tags

Starting with Spring 3, the Spring form tag library allows entering dynamic attributes, which means you

can enter any HTML5 specific attributes.

In Spring 3.1, the form input tag supports entering a type attribute other than text. This is intended

to allow rendering new HTML5 specific input types such as email, date, range, and others. Note that

entering type=text is not required since text is the default type.

18.3 Tiles

It is possible to integrate Tiles - just as any other view technology - in web applications using Spring.

The following describes in a broad way how to do this.

Note

This section focuses on Spring’s support for Tiles v3 in the

org.springframework.web.servlet.view.tiles3 package.

Dependencies

To be able to use Tiles, you have to add a dependency on Tiles version 3.0.1 or higher and its transitive

dependencies to your project.

How to integrate Tiles

To be able to use Tiles, you have to configure it using files containing definitions (for basic information

on definitions and other Tiles concepts, please have a look at http://tiles.apache.org). In Spring this is

done using the TilesConfigurer. Have a look at the following piece of example ApplicationContext

configuration:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 520

<list>

<value>/WEB-INF/defs/general.xml</value>

<value>/WEB-INF/defs/widgets.xml</value>

<value>/WEB-INF/defs/administrator.xml</value>

<value>/WEB-INF/defs/customer.xml</value>

<value>/WEB-INF/defs/templates.xml</value>

</list>

</property>

</bean>

As you can see, there are five files containing definitions, which are all located in the 'WEB-INF/

defs' directory. At initialization of the WebApplicationContext, the files will be loaded and the

definitions factory will be initialized. After that has been done, the Tiles includes in the definition files

can be used as views within your Spring web application. To be able to use the views you have to have

a ViewResolver just as with any other view technology used with Spring. Below you can find two

possibilities, the UrlBasedViewResolver and the ResourceBundleViewResolver.

You can specify locale specific Tiles definitions by adding an underscore and then the locale. For

example:

<list>

<value>/WEB-INF/defs/tiles.xml</value>

<value>/WEB-INF/defs/tiles_fr_FR.xml</value>

</list>

</property>

</bean>

With this configuration, tiles_fr_FR.xml will be used for requests with the fr_FR locale, and

tiles.xml will be used by default.

Note

Since underscores are used to indicate locales, it is recommended to avoid using them otherwise

in the file names for Tiles definitions.

UrlBasedViewResolver

The UrlBasedViewResolver instantiates the given viewClass for each view it has to resolve.

</bean>

ResourceBundleViewResolver

The ResourceBundleViewResolver has to be provided with a property file containing viewnames

and viewclasses the resolver can use:

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 521

...

welcomeView.(class)=org.springframework.web.servlet.view.tiles3.TilesView

welcomeView.url=welcome (this is the name of a Tiles definition)

vetsView.(class)=org.springframework.web.servlet.view.tiles3.TilesView

vetsView.url=vetsView (again, this is the name of a Tiles definition)

findOwnersForm.(class)=org.springframework.web.servlet.view.JstlView

findOwnersForm.url=/WEB-INF/jsp/findOwners.jsp

...

As you can see, when using the ResourceBundleViewResolver, you can easily mix different view

technologies.

Note that the TilesView class supports JSTL (the JSP Standard Tag Library) out of the box.

SimpleSpringPreparerFactory and SpringBeanPreparerFactory

As an advanced feature, Spring also supports two special Tiles PreparerFactory implementations.

Check out the Tiles documentation for details on how to use ViewPreparer references in your Tiles

definition files.

Specify SimpleSpringPreparerFactory to autowire ViewPreparer instances based on specified

preparer classes, applying Spring’s container callbacks as well as applying configured Spring

BeanPostProcessors. If Spring’s context-wide annotation-config has been activated, annotations in

ViewPreparer classes will be automatically detected and applied. Note that this expects preparer classes

in the Tiles definition files, just like the default PreparerFactory does.

Specify SpringBeanPreparerFactory to operate on specified preparer names instead of classes,

obtaining the corresponding Spring bean from the DispatcherServlet’s application context. The full bean

creation process will be in the control of the Spring application context in this case, allowing for the

use of explicit dependency injection configuration, scoped beans etc. Note that you need to define one

Spring bean definition per preparer name (as used in your Tiles definitions).

<list>

<value>/WEB-INF/defs/general.xml</value>

<value>/WEB-INF/defs/widgets.xml</value>

<value>/WEB-INF/defs/administrator.xml</value>

<value>/WEB-INF/defs/customer.xml</value>

<value>/WEB-INF/defs/templates.xml</value>

</list>

</property>

<property name="preparerFactoryClass"

value="org.springframework.web.servlet.view.tiles3.SpringBeanPreparerFactory"/>

</bean>

18.4 Velocity & FreeMarker

Velocity and FreeMarker are two templating languages that can be used as view technologies within

Spring MVC applications. The languages are quite similar and serve similar needs and so are considered

together in this section. For semantic and syntactic differences between the two languages, see the

FreeMarker web site.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 522

Dependencies

Your web application will need to include velocity-1.x.x.jar or freemarker-2.x.jar in order

to work with Velocity or FreeMarker respectively and commons-collections.jar is required for

Velocity. Typically they are included in the WEB-INF/lib folder where they are guaranteed to be found

by a Java EE server and added to the classpath for your application. It is of course assumed that you

already have the spring-webmvc.jar in your 'WEB-INF/lib' directory too! If you make use of

Spring’s dateToolAttribute or numberToolAttribute in your Velocity views, you will also need to include

the velocity-tools-generic-1.x.jar

Context configuration

A suitable configuration is initialized by adding the relevant configurer bean definition to your '*-

servlet.xml' as shown below:

<!--

This bean sets up the Velocity environment for us based on a root path for templates.

Optionally, a properties file can be specified for more control over the Velocity

environment, but the defaults are pretty sane for file based template loading.

-->

</bean>

<!--

View resolvers can also be configured with ResourceBundles or XML files. If you need

different view resolving based on Locale, you have to use the resource bundle resolver.

-->

</bean>

</bean>

<!--

View resolvers can also be configured with ResourceBundles or XML files. If you need

different view resolving based on Locale, you have to use the resource bundle resolver.

-->

</bean>

Note

For non web-apps add a VelocityConfigurationFactoryBean or a

FreeMarkerConfigurationFactoryBean to your application context definition file.

Creating templates

Your templates need to be stored in the directory specified by the *Configurer bean shown above.

This document does not cover details of creating templates for the two languages - please see their

relevant websites for information. If you use the view resolvers highlighted, then the logical view

names relate to the template file names in similar fashion to InternalResourceViewResolver for

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 523

JSP’s. So if your controller returns a ModelAndView object containing a view name of "welcome" then

the resolvers will look for the /WEB-INF/freemarker/welcome.ftl or /WEB-INF/velocity/

welcome.vm template as appropriate.

Advanced configuration

The basic configurations highlighted above will be suitable for most application requirements, however

additional configuration options are available for when unusual or advanced requirements dictate.

velocity.properties

This file is completely optional, but if specified, contains the values that are passed to the Velocity

runtime in order to configure velocity itself. Only required for advanced configurations, if you need this

file, specify its location on the VelocityConfigurer bean definition above.

</bean>

Alternatively, you can specify velocity properties directly in the bean definition for the Velocity config

bean by replacing the "configLocation" property with the following inline properties.

<props>

org.apache.velocity.runtime.resource.loader.FileResourceLoader

</prop>

<prop key="file.resource.loader.path">${webapp.root}/WEB-INF/velocity</prop>

<prop key="file.resource.loader.cache">false</prop>

</props>

</property>

</bean>

Refer to the API documentation for Spring configuration of Velocity, or the Velocity documentation for

examples and definitions of the 'velocity.properties' file itself.

FreeMarker

FreeMarker Settings and SharedVariables can be passed directly to the FreeMarker Configuration

object managed by Spring by setting the appropriate bean properties on the FreeMarkerConfigurer

bean. The freemarkerSettings property requires a java.util.Properties object and the

freemarkerVariables property requires a java.util.Map.

<map>

</map>

</property>

</bean>

See the FreeMarker documentation for details of settings and variables as they apply to the

Configuration object.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 524

Bind support and form handling

Spring provides a tag library for use in JSP’s that contains (amongst other things) a <spring:bind/>

tag. This tag primarily enables forms to display values from form backing objects and to show the results

of failed validations from a Validator in the web or business tier. From version 1.1, Spring now has

support for the same functionality in both Velocity and FreeMarker, with additional convenience macros

for generating form input elements themselves.

The bind macros

A standard set of macros are maintained within the spring-webmvc.jar file for both languages, so

they are always available to a suitably configured application.

Some of the macros defined in the Spring libraries are considered internal (private) but no such

scoping exists in the macro definitions making all macros visible to calling code and user templates.

The following sections concentrate only on the macros you need to be directly calling from within

your templates. If you wish to view the macro code directly, the files are called spring.vm /

spring.ftl and are in the packages org.springframework.web.servlet.view.velocity or

org.springframework.web.servlet.view.freemarker respectively.

Simple binding

In your html forms (vm / ftl templates) that act as the formView for a Spring form controller, you can

use code similar to the following to bind to field values and display error messages for each input field

in similar fashion to the JSP equivalent. Note that the name of the command object is "command" by

default, but can be overridden in your MVC configuration by setting the commandName bean property

on your form controller. Example code is shown below for the personFormV and personFormF views

configured earlier;

<html>

...

Name:

#springBind( "command.name" )

<input type="text"

name="${status.expression}"

value="$!status.value" /><br>

#foreach($error in $status.errorMessages) <b>$error</b> <br> #end

<br>

...

</form>

...

</html>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 525

<!-- freemarker macros have to be imported into a namespace. We strongly

recommend sticking to spring -->

<#import "/spring.ftl" as spring />

<html>

...

Name:

<@spring.bind "command.name" />

<input type="text"

name="${spring.status.expression}"

value="${spring.status.value?default("")}" /><br>

<#list spring.status.errorMessages as error> <b>${error}</b> <br> </#list>

<br>

...

</form>

...

</html>

#springBind / <@spring.bind> requires a path argument which consists of the name of your

command object (it will be command unless you changed it in your FormController properties) followed

by a period and the name of the field on the command object you wish to bind to. Nested fields can

be used too such as "command.address.street". The bind macro assumes the default HTML escaping

behavior specified by the ServletContext parameter defaultHtmlEscape in web.xml

The optional form of the macro called #springBindEscaped / <@spring.bindEscaped> takes a

second argument and explicitly specifies whether HTML escaping should be used in the status error

messages or values. Set to true or false as required. Additional form handling macros simplify the use

of HTML escaping and these macros should be used wherever possible. They are explained in the next

section.

Form input generation macros

Additional convenience macros for both languages simplify both binding and form generation (including

validation error display). It is never necessary to use these macros to generate form input fields, and

they can be mixed and matched with simple HTML or calls direct to the spring bind macros highlighted

previously.

The following table of available macros show the VTL and FTL definitions and the parameter list that

each takes.

Table 18.1. Table of macro definitions

macro VTL definition FTL definition

message (output a string from a resource bundle based on

the code parameter)

#springMessage($code)<@spring.message

code/>

messageText (output a string from a resource bundle

based on the code parameter, falling back to the value of

the default parameter)

#springMessageText($code

$text)

<@spring.messageText

code, text/>

url (prefix a relative URL with the application’s context

root)

#springUrl($relativeUrl)<@spring.url

relativeUrl/>

formInput (standard input field for gathering user input) #springFormInput($path

$attributes)

<@spring.formInput

path, attributes,

fieldType/>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 526

macro VTL definition FTL definition

formHiddenInput * (hidden input field for submitting non-

user input)

#springFormHiddenInput($path

$attributes)

<@spring.formHiddenInput

path, attributes/>

formPasswordInput * (standard input field for gathering

passwords. Note that no value will ever be populated in

fields of this type)

#springFormPasswordInput($path

$attributes)

<@spring.formPasswordInput

path, attributes/>

formTextarea (large text field for gathering long, freeform

text input)

#springFormTextarea($path

$attributes)

<@spring.formTextarea

path, attributes/>

formSingleSelect (drop down box of options allowing a

single required value to be selected)

#springFormSingleSelect( $path

$options

$attributes)

<@spring.formSingleSelect

path, options,

attributes/>

formMultiSelect (a list box of options allowing the user to

select 0 or more values)

#springFormMultiSelect($path

$options

$attributes)

<@spring.formMultiSelect

path, options,

attributes/>

formRadioButtons (a set of radio buttons allowing a

single selection to be made from the available choices)

#springFormRadioButtons($path

$options

$separator

$attributes)

<@spring.formRadioButtons

path, options

separator,

attributes/>

formCheckboxes (a set of checkboxes allowing 0 or more

values to be selected)

#springFormCheckboxes($path

$options

$separator

$attributes)

<@spring.formCheckboxes

path, options,

separator,

attributes/>

formCheckbox (a single checkbox) #springFormCheckbox($path

$attributes)

<@spring.formCheckbox

path, attributes/>

showErrors (simplify display of validation errors for the

bound field)

#springShowErrors($separator

$classOrStyle)

<@spring.showErrors

separator,

classOrStyle/>

• In FTL (FreeMarker), these two macros are not actually required as you can use the normal

formInput macro, specifying ' hidden' or ' password' as the value for the fieldType parameter.

The parameters to any of the above macros have consistent meanings:

• path: the name of the field to bind to (ie "command.name")

• options: a Map of all the available values that can be selected from in the input field. The keys to

the map represent the values that will be POSTed back from the form and bound to the command

object. Map objects stored against the keys are the labels displayed on the form to the user and may

be different from the corresponding values posted back by the form. Usually such a map is supplied

as reference data by the controller. Any Map implementation can be used depending on required

behavior. For strictly sorted maps, a SortedMap such as a TreeMap with a suitable Comparator may

be used and for arbitrary Maps that should return values in insertion order, use a LinkedHashMap

or a LinkedMap from commons-collections.

• separator: where multiple options are available as discreet elements (radio buttons or checkboxes),

the sequence of characters used to separate each one in the list (ie "<br>").

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 527

• attributes: an additional string of arbitrary tags or text to be included within the HTML tag itself. This

string is echoed literally by the macro. For example, in a textarea field you may supply attributes as

rows="5" cols="60" or you could pass style information such as style="border:1px solid silver".

• classOrStyle: for the showErrors macro, the name of the CSS class that the span tag wrapping each

error will use. If no information is supplied (or the value is empty) then the errors will be wrapped in

<b></b> tags.

Examples of the macros are outlined below some in FTL and some in VTL. Where usage differences

exist between the two languages, they are explained in the notes.

Input Fields

...

Name:

#springFormInput("command.name" "")<br>

#springShowErrors("<br>" "")<br>

The formInput macro takes the path parameter (command.name) and an additional attributes parameter

which is empty in the example above. The macro, along with all other form generation macros, performs

an implicit spring bind on the path parameter. The binding remains valid until a new bind occurs so the

showErrors macro doesn’t need to pass the path parameter again - it simply operates on whichever

field a bind was last created for.

The showErrors macro takes a separator parameter (the characters that will be used to separate multiple

errors on a given field) and also accepts a second parameter, this time a class name or style attribute.

Note that FreeMarker is able to specify default values for the attributes parameter, unlike Velocity, and

the two macro calls above could be expressed as follows in FTL:

<@spring.formInput "command.name"/>

<@spring.showErrors "<br>"/>

Output is shown below of the form fragment generating the name field, and displaying a validation error

after the form was submitted with no value in the field. Validation occurs through Spring’s Validation

framework.

The generated HTML looks like this:

Name:

<br>

<b>required</b>

<br>

The formTextarea macro works the same way as the formInput macro and accepts the same parameter

list. Commonly, the second parameter (attributes) will be used to pass style information or rows and

cols attributes for the textarea.

Selection Fields

Four selection field macros can be used to generate common UI value selection inputs in your HTML

forms.

• formSingleSelect

• formMultiSelect

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 528

• formRadioButtons

• formCheckboxes

Each of the four macros accepts a Map of options containing the value for the form field, and the label

corresponding to that value. The value and the label can be the same.

An example of radio buttons in FTL is below. The form backing object specifies a default value of London

for this field and so no validation is necessary. When the form is rendered, the entire list of cities to

choose from is supplied as reference data in the model under the name cityMap.

...

Town:

<@spring.formRadioButtons "command.address.town", cityMap, "" /><br><br>

This renders a line of radio buttons, one for each value in cityMap using the separator "". No additional

attributes are supplied (the last parameter to the macro is missing). The cityMap uses the same String

for each key-value pair in the map. The map’s keys are what the form actually submits as POSTed

request parameters, map values are the labels that the user sees. In the example above, given a list of

three well known cities and a default value in the form backing object, the HTML would be

Town:

<input type="radio" name="address.town" value="London">London</input>

<input type="radio" name="address.town" value="Paris" checked="checked">Paris</input>

If your application expects to handle cities by internal codes for example, the map of codes would be

created with suitable keys like the example below.

protected Map referenceData(HttpServletRequest request) throws Exception {

Map cityMap = new LinkedHashMap();

cityMap.put("LDN", "London");

cityMap.put("PRS", "Paris");

cityMap.put("NYC", "New York");

Map m = new HashMap();

m.put("cityMap", cityMap);

return m;

}

The code would now produce output where the radio values are the relevant codes but the user still

sees the more user friendly city names.

Town:

<input type="radio" name="address.town" value="LDN">London</input>

<input type="radio" name="address.town" value="PRS" checked="checked">Paris</input>

HTML escaping and XHTML compliance

Default usage of the form macros above will result in HTML tags that are HTML 4.01 compliant and

that use the default value for HTML escaping defined in your web.xml as used by Spring’s bind support.

In order to make the tags XHTML compliant or to override the default HTML escaping value, you can

specify two variables in your template (or in your model where they will be visible to your templates).

The advantage of specifying them in the templates is that they can be changed to different values later

in the template processing to provide different behavior for different fields in your form.

To switch to XHTML compliance for your tags, specify a value of true for a model/context variable named

xhtmlCompliant:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 529

# for Velocity..

#set($springXhtmlCompliant = true)

<-- for FreeMarker -->

<#assign xhtmlCompliant = true in spring>

Any tags generated by the Spring macros will now be XHTML compliant after processing this directive.

In similar fashion, HTML escaping can be specified per field:

<#-- until this point, default HTML escaping is used -->

<#assign htmlEscape = true in spring>

<#-- next field will use HTML escaping -->

<@spring.formInput "command.name" />

<#assign htmlEscape = false in spring>

<#-- all future fields will be bound with HTML escaping off -->

18.5 XSLT

XSLT is a transformation language for XML and is popular as a view technology within web applications.

XSLT can be a good choice as a view technology if your application naturally deals with XML, or if your

model can easily be converted to XML. The following section shows how to produce an XML document

as model data and have it transformed with XSLT in a Spring Web MVC application.

My First Words

This example is a trivial Spring application that creates a list of words in the Controller and adds them

to the model map. The map is returned along with the view name of our XSLT view. See Section 17.3,

“Implementing Controllers” for details of Spring Web MVC’s Controller interface. The XSLT view will

turn the list of words into a simple XML document ready for transformation.

Bean definitions

Configuration is standard for a simple Spring application. The dispatcher servlet config file contains a

reference to a ViewResolver, URL mappings and a single controller bean…

i. that encapsulates our word generation logic.

Standard MVC controller code

The controller logic is encapsulated in a subclass of AbstractController, with the handler method

being defined like so…

protected ModelAndView handleRequestInternal(HttpServletRequest request,

HttpServletResponse response) throws Exception {

Map map = new HashMap();

List wordList = new ArrayList();

wordList.add("hello");

wordList.add("world");

map.put("wordList", wordList);

return new ModelAndView("home", map);

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 530

So far we’ve done nothing that’s XSLT specific. The model data has been created in the same way as

you would for any other Spring MVC application. Depending on the configuration of the application now,

that list of words could be rendered by JSP/JSTL by having them added as request attributes, or they

could be handled by Velocity by adding the object to the VelocityContext. In order to have XSLT

render them, they of course have to be converted into an XML document somehow. There are software

packages available that will automatically domify an object graph, but within Spring, you have complete

flexibility to create the DOM from your model in any way you choose. This prevents the transformation

of XML playing too great a part in the structure of your model data which is a danger when using tools

to manage the domification process.

Convert the model data to XML

In order to create a DOM document from our list of words or any other model data, we must subclass

the (provided) org.springframework.web.servlet.view.xslt.AbstractXsltView class. In

doing so, we must also typically implement the abstract method createXsltSource(..) method. The

first parameter passed to this method is our model map. Here’s the complete listing of the HomePage

class in our trivial word application:

package xslt;

// imports omitted for brevity

public class HomePage extends AbstractXsltView {

protected Source createXsltSource(Map model, String rootName,

HttpServletRequest request, HttpServletResponse response) throws Exception {

Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();

Element root = document.createElement(rootName);

List words = (List) model.get("wordList");

for (Iterator it = words.iterator(); it.hasNext();) {

String nextWord = (String) it.next();

Element wordNode = document.createElement("word");

Text textNode = document.createTextNode(nextWord);

wordNode.appendChild(textNode);

root.appendChild(wordNode);

}

return new DOMSource(root);

}

A series of parameter name/value pairs can optionally be defined by your subclass which will be

added to the transformation object. The parameter names must match those defined in your XSLT

template declared with <xsl:param name="myParam">defaultValue</xsl:param>. To specify

the parameters, override the getParameters() method of the AbstractXsltView class and return

a Map of the name/value pairs. If your parameters need to derive information from the current request,

you can override the getParameters(HttpServletRequest request) method instead.

Defining the view properties

The views.properties file (or equivalent xml definition if you’re using an XML based view resolver as we

did in the Velocity examples above) looks like this for the one-view application that is My First Words:

home.(class)=xslt.HomePage

home.stylesheetLocation=/WEB-INF/xsl/home.xslt

home.root=words

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 531

Here, you can see how the view is tied in with the HomePage class just written which handles the model

domification in the first property '.(class)'. The 'stylesheetLocation' property points to the

XSLT file which will handle the XML transformation into HTML for us and the final property '.root' is

the name that will be used as the root of the XML document. This gets passed to the HomePage class

above in the second parameter to the createXsltSource(..) method(s).

Document transformation

Finally, we have the XSLT code used for transforming the above document. As shown in the above

'views.properties' file, the stylesheet is called 'home.xslt' and it lives in the war file in the

'WEB-INF/xsl' directory.

<?xml version="1.0" encoding="utf-8"?>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="html" omit-xml-declaration="yes"/>

<xsl:template match="/">

<html>

<head><title>Hello!</title></head>

<body>

<h1>My First Words</h1>

<xsl:apply-templates/>

</body>

</html>

</xsl:template>

<xsl:template match="word">

<xsl:value-of select="."/><br/>

</xsl:template>

</xsl:stylesheet>

Summary

A summary of the files discussed and their location in the WAR file is shown in the simplified WAR

structure below.

ProjectRoot

+- WebContent

+- WEB-INF

+- classes

| |

| +- xslt

| | |

| | +- HomePageController.class

| | +- HomePage.class

| |

| +- views.properties

+- lib

| |

| +- spring-*.jar

+- xsl

| |

| +- home.xslt

+- frontcontroller-servlet.xml

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 532

You will also need to ensure that an XML parser and an XSLT engine are available on the classpath.

JDK 1.4 provides them by default, and most Java EE containers will also make them available by default,

but it’s a possible source of errors to be aware of.

18.6 Document views (PDF/Excel)

Introduction

Returning an HTML page isn’t always the best way for the user to view the model output, and Spring

makes it simple to generate a PDF document or an Excel spreadsheet dynamically from the model

data. The document is the view and will be streamed from the server with the correct content type to

(hopefully) enable the client PC to run their spreadsheet or PDF viewer application in response.

In order to use Excel views, you need to add the poi library to your classpath, and for PDF generation,

the iText library.

Configuration and setup

Document based views are handled in an almost identical fashion to XSLT views, and the following

sections build upon the previous one by demonstrating how the same controller used in the XSLT

example is invoked to render the same model as both a PDF document and an Excel spreadsheet

(which can also be viewed or manipulated in Open Office).

Document view definitions

First, let’s amend the views.properties file (or xml equivalent) and add a simple view definition for both

document types. The entire file now looks like this with the XSLT view shown from earlier:

home.(class)=xslt.HomePage

home.stylesheetLocation=/WEB-INF/xsl/home.xslt

home.root=words

xl.(class)=excel.HomePage

pdf.(class)=pdf.HomePage

If you want to start with a template spreadsheet or a fillable PDF form to add your model data to, specify

the location as the url property in the view definition

Controller code

The controller code we’ll use remains exactly the same from the XSLT example earlier other than to

change the name of the view to use. Of course, you could be clever and have this selected based on

a URL parameter or some other logic - proof that Spring really is very good at decoupling the views

from the controllers!

Subclassing for Excel views

Exactly as we did for the XSLT example, we’ll subclass suitable abstract classes in order to

implement custom behavior in generating our output documents. For Excel, this involves writing

a subclass of org.springframework.web.servlet.view.document.AbstractExcelView

(for Excel files generated by POI) or

org.springframework.web.servlet.view.document.AbstractJExcelView (for JExcelApi-

generated Excel files) and implementing the buildExcelDocument() method.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 533

Here’s the complete listing for our POI Excel view which displays the word list from the model map in

consecutive rows of the first column of a new spreadsheet:

package excel;

// imports omitted for brevity

public class HomePage extends AbstractExcelView {

protected void buildExcelDocument(Map model, HSSFWorkbook wb, HttpServletRequest req,

HttpServletResponse resp) throws Exception {

HSSFSheet sheet;

HSSFRow sheetRow;

HSSFCell cell;

// Go to the first sheet

// getSheetAt: only if wb is created from an existing document

// sheet = wb.getSheetAt(0);

sheet = wb.createSheet("Spring");

sheet.setDefaultColumnWidth((short) 12);

// write a text at A1

cell = getCell(sheet, 0, 0);

setText(cell, "Spring-Excel test");

List words = (List) model.get("wordList");

for (int i=0; i < words.size(); i++) {

cell = getCell(sheet, 2+i, 0);

setText(cell, (String) words.get(i));

}

And the following is a view generating the same Excel file, now using JExcelApi:

package excel;

// imports omitted for brevity

public class HomePage extends AbstractJExcelView {

protected void buildExcelDocument(Map model, WritableWorkbook wb,

HttpServletRequest request, HttpServletResponse response) throws Exception {

WritableSheet sheet = wb.createSheet("Spring", 0);

sheet.addCell(new Label(0, 0, "Spring-Excel test"));

List words = (List) model.get("wordList");

for (int i = 0; i < words.size(); i++) {

sheet.addCell(new Label(2+i, 0, (String) words.get(i)));

}

Note the differences between the APIs. We’ve found that the JExcelApi is somewhat more intuitive,

and furthermore, JExcelApi has slightly better image-handling capabilities. There have been memory

problems with large Excel files when using JExcelApi however.

If you now amend the controller such that it returns xl as the name of the view ( return new

ModelAndView("xl", map);) and run your application again, you should find that the Excel

spreadsheet is created and downloaded automatically when you request the same page as before.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 534

Subclassing for PDF views

The PDF version of the word list is even simpler. This time, the class extends

org.springframework.web.servlet.view.document.AbstractPdfView and implements

the buildPdfDocument() method as follows:

package pdf;

// imports omitted for brevity

public class PDFPage extends AbstractPdfView {

protected void buildPdfDocument(Map model, Document doc, PdfWriter writer,

HttpServletRequest req, HttpServletResponse resp) throws Exception {

List words = (List) model.get("wordList");

for (int i=0; i<words.size(); i++) {

doc.add( new Paragraph((String) words.get(i)));

}

Once again, amend the controller to return the pdf view with return new ModelAndView("pdf",

map);, and reload the URL in your application. This time a PDF document should appear listing each

of the words in the model map.

18.7 JasperReports

JasperReports ( http://jasperreports.sourceforge.net) is a powerful open-source reporting engine that

supports the creation of report designs using an easily understood XML file format. JasperReports is

capable of rendering reports in four different formats: CSV, Excel, HTML and PDF.

Dependencies

Your application will need to include the latest release of JasperReports, which at the time of writing

was 0.6.1. JasperReports itself depends on the following projects:

• BeanShell

• Commons BeanUtils

• Commons Collections

• Commons Digester

• Commons Logging

• iText

• POI

JasperReports also requires a JAXP compliant XML parser.

Configuration

To configure JasperReports views in your Spring container configuration you need to define a

ViewResolver to map view names to the appropriate view class depending on which format you want

your report rendered in.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 535

Configuring the ViewResolver

Typically, you will use the ResourceBundleViewResolver to map view names to view classes and

files in a properties file.

</bean>

Here we’ve configured an instance of the ResourceBundleViewResolver class that will look for view

mappings in the resource bundle with base name views. (The content of this file is described in the

next section.)

Configuring the Views

The Spring Framework contains five different View implementations for JasperReports, four of which

correspond to one of the four output formats supported by JasperReports, and one that allows for the

format to be determined at runtime:

Table 18.2. JasperReports View classes

Class Name Render Format

JasperReportsCsvView CSV

JasperReportsHtmlView HTML

JasperReportsPdfView PDF

JasperReportsXlsView Microsoft Excel

JasperReportsMultiFormatView The view is decided upon at runtime

Mapping one of these classes to a view name and a report file is a matter of adding the appropriate

entries in the resource bundle configured in the previous section as shown here:

simpleReport.(class)=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView

simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper

Here you can see that the view with name simpleReport is mapped to the JasperReportsPdfView

class, causing the output of this report to be rendered in PDF format. The url property of the view is

set to the location of the underlying report file.

About Report Files

JasperReports has two distinct types of report file: the design file, which has a .jrxml extension, and

the compiled report file, which has a .jasper extension. Typically, you use the JasperReports Ant task

to compile your .jrxml design file into a .jasper file before deploying it into your application. With the

Spring Framework you can map either of these files to your report file and the framework will take care

of compiling the .jrxml file on the fly for you. You should note that after a .jrxml file is compiled by

the Spring Framework, the compiled report is cached for the lifetime of the application. Thus, to make

changes to the file you will need to restart your application.

Using JasperReportsMultiFormatView

The JasperReportsMultiFormatView allows for the report format to be specified at runtime. The

actual rendering of the report is delegated to one of the other JasperReports view classes - the

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 536

JasperReportsMultiFormatView class simply adds a wrapper layer that allows for the exact

implementation to be specified at runtime.

The JasperReportsMultiFormatView class introduces two concepts: the format key and the

discriminator key. The JasperReportsMultiFormatView class uses the mapping key to look up

the actual view implementation class, and it uses the format key to lookup up the mapping key. From

a coding perspective you add an entry to your model with the format key as the key and the mapping

key as the value, for example:

public ModelAndView handleSimpleReportMulti(HttpServletRequest request,

HttpServletResponse response) throws Exception {

String uri = request.getRequestURI();

String format = uri.substring(uri.lastIndexOf(".") + 1);

Map model = getModel();

model.put("format", format);

return new ModelAndView("simpleReportMulti", model);

}

In this example, the mapping key is determined from the extension of the request URI and is added to

the model under the default format key: format. If you wish to use a different format key then you can

configure this using the formatKey property of the JasperReportsMultiFormatView class.

By default the following mapping key mappings are configured in JasperReportsMultiFormatView:

Table 18.3. JasperReportsMultiFormatView Default Mapping Key Mappings

Mapping Key View Class

csv JasperReportsCsvView

html JasperReportsHtmlView

pdf JasperReportsPdfView

xls JasperReportsXlsView

So in the example above a request to URI /foo/myReport.pdf would be mapped to the

JasperReportsPdfView class. You can override the mapping key to view class mappings using the

formatMappings property of JasperReportsMultiFormatView.

Populating the ModelAndView

In order to render your report correctly in the format you have chosen, you must supply Spring with all

of the data needed to populate your report. For JasperReports this means you must pass in all report

parameters along with the report datasource. Report parameters are simple name/value pairs and can

be added to the Map for your model as you would add any name/value pair.

When adding the datasource to the model you have two approaches to choose from. The first approach

is to add an instance of JRDataSource or a Collection type to the model Map under any arbitrary

key. Spring will then locate this object in the model and treat it as the report datasource. For example,

you may populate your model like so:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 537

private Map getModel() {

Map model = new HashMap();

Collection beanData = getBeanData();

model.put("myBeanData", beanData);

return model;

}

The second approach is to add the instance of JRDataSource or Collection under a specific key

and then configure this key using the reportDataKey property of the view class. In both cases Spring

will wrap instances of Collection in a JRBeanCollectionDataSource instance. For example:

private Map getModel() {

Map model = new HashMap();

Collection beanData = getBeanData();

Collection someData = getSomeData();

model.put("myBeanData", beanData);

model.put("someData", someData);

return model;

}

Here you can see that two Collection instances are being added to the model. To ensure that the

correct one is used, we simply modify our view configuration as appropriate:

simpleReport.(class)=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView

simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper

simpleReport.reportDataKey=myBeanData

Be aware that when using the first approach, Spring will use the first instance of JRDataSource

or Collection that it encounters. If you need to place multiple instances of JRDataSource or

Collection into the model you need to use the second approach.

Working with Sub-Reports

JasperReports provides support for embedded sub-reports within your master report files. There are a

wide variety of mechanisms for including sub-reports in your report files. The easiest way is to hard code

the report path and the SQL query for the sub report into your design files. The drawback of this approach

is obvious: the values are hard-coded into your report files reducing reusability and making it harder to

modify and update report designs. To overcome this you can configure sub-reports declaratively, and

you can include additional data for these sub-reports directly from your controllers.

Configuring Sub-Report Files

To control which sub-report files are included in a master report using Spring, your report file must be

configured to accept sub-reports from an external source. To do this you declare a parameter in your

report file like so:

Then, you define your sub-report to use this sub-report parameter:

<reportElement isPrintRepeatedValues="false" x="5" y="25" width="325"

height="20" isRemoveLineWhenBlank="true" backcolor="#ffcc99"/>

</subreportParameter>

<![CDATA[$P{ProductsSubReport}]]></subreportExpression>

</subreport>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 538

This defines a master report file that expects the sub-report to be passed in as an instance of

net.sf.jasperreports.engine.JasperReports under the parameter ProductsSubReport.

When configuring your Jasper view class, you can instruct Spring to load a report file and pass it into

the JasperReports engine as a sub-report using the subReportUrls property:

<map>

</map>

</property>

Here, the key of the Map corresponds to the name of the sub-report parameter in the report design file,

and the entry is the URL of the report file. Spring will load this report file, compiling it if necessary, and

pass it into the JasperReports engine under the given key.

Configuring Sub-Report Data Sources

This step is entirely optional when using Spring to configure your sub-reports. If you wish, you can

still configure the data source for your sub-reports using static queries. However, if you want Spring

to convert data returned in your ModelAndView into instances of JRDataSource then you need to

specify which of the parameters in your ModelAndView Spring should convert. To do this, configure

the list of parameter names using the subReportDataKeys property of your chosen view class:

Here, the key you supply must correspond to both the key used in your ModelAndView and the key

used in your report design file.

Configuring Exporter Parameters

If you have special requirements for exporter configuration — perhaps you want a specific page

size for your PDF report — you can configure these exporter parameters declaratively in your

Spring configuration file using the exporterParameters property of the view class. The

exporterParameters property is typed as a Map. In your configuration the key of an entry should be

the fully-qualified name of a static field that contains the exporter parameter definition, and the value of

an entry should be the value you want to assign to the parameter. An example of this is shown below:

<map>

<value>Footer by Spring!

</td><td width="50%">&nbsp; </td></tr>

</table></body></html>

</value>

</entry>

</map>

</property>

</bean>

Here you can see that the JasperReportsHtmlView is configured with an exporter parameter for

net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER which

will output a footer in the resulting HTML.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 539

18.8 Feed Views

Both AbstractAtomFeedView and AbstractRssFeedView inherit from the base class

AbstractFeedView and are used to provide Atom and RSS Feed views respectfully.

They are based on java.net’s ROME project and are located in the package

org.springframework.web.servlet.view.feed.

AbstractAtomFeedView requires you to implement the buildFeedEntries() method and

optionally override the buildFeedMetadata() method (the default implementation is empty), as

shown below.

public class SampleContentAtomView extends AbstractAtomFeedView {

@Override

protected void buildFeedMetadata(Map<String, Object> model,

Feed feed, HttpServletRequest request) {

// implementation omitted

}

@Override

protected List<Entry> buildFeedEntries(Map<String, Object> model,

HttpServletRequest request, HttpServletResponse response) throws Exception {

// implementation omitted

}

Similar requirements apply for implementing AbstractRssFeedView, as shown below.

public class SampleContentAtomView extends AbstractRssFeedView {

@Override

protected void buildFeedMetadata(Map<String, Object> model,

Channel feed, HttpServletRequest request) {

// implementation omitted

}

@Override

protected List<Item> buildFeedItems(Map<String, Object> model,

HttpServletRequest request, HttpServletResponse response) throws Exception {

// implementation omitted

}

The buildFeedItems() and buildFeedEntires() methods pass in the HTTP request in case you

need to access the Locale. The HTTP response is passed in only for the setting of cookies or other

HTTP headers. The feed will automatically be written to the response object after the method returns.

For an example of creating an Atom view please refer to Alef Arendsen’s Spring Team Blog entry.

18.9 XML Marshalling View

The MarshallingView uses an XML Marshaller defined in the org.springframework.oxm

package to render the response content as XML. The object to be marshalled can be set explicitly

using MarhsallingView's modelKey bean property. Alternatively, the view will iterate over all model

properties and marshal the first type that is supported by the Marshaller. For more information on

the functionality in the org.springframework.oxm package refer to the chapter Marshalling XML

using O/X Mappers.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 540

18.10 JSON Mapping View

The MappingJackson2JsonView uses the Jackson library’s ObjectMapper to render the response

content as JSON. By default, the entire contents of the model map (with the exception of framework-

specific classes) will be encoded as JSON. For cases where the contents of the map need to be filtered,

users may specify a specific set of model attributes to encode via the RenderedAttributes property.

The extractValueFromSingleKeyModel property may also be used to have the value in single-

key models extracted and serialized directly rather than as a map of model attributes.

JSON mapping can be customized as needed through the use of Jackson’s provided annotations.

When further control is needed, a custom ObjectMapper can be injected through the ObjectMapper

property for cases where custom JSON serializers/deserializers need to be provided for specific types.

JSONP is supported and automatically enabled when the request has a query parameter named

jsonp or callback. The JSONP query parameter name(s) could be customized through the

jsonpParameterNames property.

18.11 XML Mapping View

The MappingJackson2XmlView uses the Jackson XML extension's XmlMapper to render the

response content as XML. If the model contains multiples entries, the object to be serialized should be

set explicitly using MappingJackson2XmlView's modelKey bean property. If the model contains a

single entry, it will be serialized automatically.

XML mapping can be customized as needed through the use of JAXB or Jackson’s provided

annotations. When further control is needed, a custom XmlMapper can be injected through the

ObjectMapper property for cases where custom XML serializers/deserializers need to be provided

for specific types.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 541

19. Integrating with other web frameworks

19.1 Introduction

Spring Web Flow

Spring Web Flow (SWF) aims to be the best solution for the management of web application page

flow.

SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and

Portlet environments. If you have a business process (or processes) that would benefit from a

conversational model as opposed to a purely request model, then SWF may be the solution.

SWF allows you to capture logical page flows as self-contained modules that are reusable in

different situations, and as such is ideal for building web application modules that guide the user

through controlled navigations that drive business processes.

For more information about SWF, consult the Spring Web Flow website.

This chapter details Spring’s integration with third party web frameworks, such as JSF.

One of the core value propositions of the Spring Framework is that of enabling choice. In a general

sense, Spring does not force one to use or buy into any particular architecture, technology, or

methodology (although it certainly recommends some over others). This freedom to pick and choose

the architecture, technology, or methodology that is most relevant to a developer and their development

team is arguably most evident in the web area, where Spring provides its own web framework (Spring

MVC), while at the same time providing integration with a number of popular third party web frameworks.

This allows one to continue to leverage any and all of the skills one may have acquired in a particular

web framework such as JSF, while at the same time being able to enjoy the benefits afforded by Spring

in other areas such as data access, declarative transaction management, and flexible configuration and

application assembly.

Having dispensed with the woolly sales patter (c.f. the previous paragraph), the remainder of this chapter

will concentrate upon the meaty details of integrating your favorite web framework with Spring. One thing

that is often commented upon by developers coming to Java from other languages is the seeming super-

abundance of web frameworks available in Java. There are indeed a great number of web frameworks

in the Java space; in fact there are far too many to cover with any semblance of detail in a single

chapter. This chapter thus picks four of the more popular web frameworks in Java, starting with the

Spring configuration that is common to all of the supported web frameworks, and then detailing the

specific integration options for each supported web framework.

Note

Please note that this chapter does not attempt to explain how to use any of the supported web

frameworks. For example, if you want to use JSF for the presentation layer of your web application,

the assumption is that you are already familiar with JSF itself. If you need further details about

any of the supported web frameworks themselves, please do consult Section 19.6, “Further

Resources” at the end of this chapter.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 542

19.2 Common configuration

Before diving into the integration specifics of each supported web framework, let us first take a look at

the Spring configuration that is not specific to any one web framework. (This section is equally applicable

to Spring’s own web framework, Spring MVC.)

One of the concepts (for want of a better word) espoused by (Spring’s) lightweight application model is

that of a layered architecture. Remember that in a classic layered architecture, the web layer is but one of

many layers; it serves as one of the entry points into a server side application and it delegates to service

objects (facades) defined in a service layer to satisfy business specific (and presentation-technology

agnostic) use cases. In Spring, these service objects, any other business-specific objects, data access

objects, etc. exist in a distinct business context, which contains no web or presentation layer objects

(presentation objects such as Spring MVC controllers are typically configured in a distinct presentation

context). This section details how one configures a Spring container (a WebApplicationContext)

that contains all of the business beans in one’s application.

On to specifics: all that one need do is to declare a ContextLoaderListener in the standard Java EE

servlet web.xml file of one’s web application, and add a contextConfigLocation<context-param/

> section (in the same file) that defines which set of Spring XML configuration files to load.

Find below the <listener/> configuration:

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

Find below the <context-param/> configuration:

<context-param>

<param-name>contextConfigLocation</param-name>

<param-value>/WEB-INF/applicationContext*.xml</param-value>

</context-param>

If you don’t specify the contextConfigLocation context parameter, the

ContextLoaderListener will look for a file called /WEB-INF/applicationContext.xml to load.

Once the context files are loaded, Spring creates a WebApplicationContext object based on the

bean definitions and stores it in the ServletContext of the web application.

All Java web frameworks are built on top of the Servlet API, and so one can use the following

code snippet to get access to this business context ApplicationContext created by the

ContextLoaderListener.

WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);

The WebApplicationContextUtils class is for convenience, so you don’t

have to remember the name of the ServletContext attribute. Its

getWebApplicationContext() method will return null if an object doesn’t exist under

the WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key. Rather

than risk getting NullPointerExceptions in your application, it’s better to use the

getRequiredWebApplicationContext() method. This method throws an exception when the

ApplicationContext is missing.

Once you have a reference to the WebApplicationContext, you can retrieve beans by their name or

type. Most developers retrieve beans by name and then cast them to one of their implemented interfaces.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 543

Fortunately, most of the frameworks in this section have simpler ways of looking up beans. Not only

do they make it easy to get beans from a Spring container, but they also allow you to use dependency

injection on their controllers. Each web framework section has more detail on its specific integration

strategies.

19.3 JavaServer Faces 1.2

JavaServer Faces (JSF) is the JCP’s standard component-based, event-driven web user interface

framework. As of Java EE 5, it is an official part of the Java EE umbrella.

For a popular JSF runtime as well as for popular JSF component libraries, check out the Apache

MyFaces project. The MyFaces project also provides common JSF extensions such as MyFaces

Orchestra: a Spring-based JSF extension that provides rich conversation scope support.

Note

Spring Web Flow 2.0 provides rich JSF support through its newly established Spring Faces

module, both for JSF-centric usage (as described in this section) and for Spring-centric usage

(using JSF views within a Spring MVC dispatcher). Check out the Spring Web Flow website for

details!

The key element in Spring’s JSF integration is the JSF ELResolver mechanism.

SpringBeanFacesELResolver (JSF 1.2+)

SpringBeanFacesELResolver is a JSF 1.2 compliant ELResolver implementation, integrating with

the standard Unified EL as used by JSF 1.2 and JSP 2.1. Like SpringBeanVariableResolver, it

delegates to the Spring’s business context WebApplicationContext first, then to the default resolver

of the underlying JSF implementation.

Configuration-wise, simply define SpringBeanFacesELResolver in your JSF 1.2 faces-context.xml

file:

<faces-config>

<el-resolver>org.springframework.web.jsf.el.SpringBeanFacesELResolver</el-resolver>

...

</application>

</faces-config>

FacesContextUtils

A custom VariableResolver works well when mapping one’s properties to beans in faces-config.xml,

but at times one may need to grab a bean explicitly. The FacesContextUtils class makes this easy. It

is similar to WebApplicationContextUtils, except that it takes a FacesContext parameter rather

than a ServletContext parameter.

ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());

19.4 Apache Struts 2.x

Invented by Craig McClanahan, Struts is an open source project hosted by the Apache Software

Foundation. At the time, it greatly simplified the JSP/Servlet programming paradigm and won over many

developers who were using proprietary frameworks. It simplified the programming model, it was open

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 544

source (and thus free as in beer), and it had a large community, which allowed the project to grow and

become popular among Java web developers.

Check out the Struts Spring Plugin for the built-in Spring integration shipped with Struts.

19.5 Tapestry 5.x

From the Tapestry homepage:

Tapestry is a "Component oriented framework for creating dynamic, robust, highly scalable web

applications in Java."

While Spring has its own powerful web layer, there are a number of unique advantages to building an

enterprise Java application using a combination of Tapestry for the web user interface and the Spring

container for the lower layers.

For more information, check out Tapestry’s dedicated integration module for Spring.

19.6 Further Resources

Find below links to further resources about the various web frameworks described in this chapter.

• The JSF homepage

• The Struts homepage

• The Tapestry homepage

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 545

20. Portlet MVC Framework

20.1 Introduction

JSR-168 The Java Portlet Specification

For more general information about portlet development, please review a whitepaper from Oracle

entitled "Introduction to JSR 168", and of course the JSR-168 Specification itself.

In addition to supporting conventional (servlet-based) Web development, Spring also supports JSR-168

Portlet development. As much as possible, the Portlet MVC framework is a mirror image of the Web MVC

framework, and also uses the same underlying view abstractions and integration technology. So, be sure

to review the chapters entitled Chapter 17, Web MVC framework and Chapter 18, View technologies

before continuing with this chapter.

Note

Bear in mind that while the concepts of Spring MVC are the same in Spring Portlet MVC, there

are some notable differences created by the unique workflow of JSR-168 portlets.

The main way in which portlet workflow differs from servlet workflow is that the request to the portlet

can have two distinct phases: the action phase and the render phase. The action phase is executed

only once and is where any backend changes or actions occur, such as making changes in a database.

The render phase then produces what is displayed to the user each time the display is refreshed. The

critical point here is that for a single overall request, the action phase is executed only once, but the

render phase may be executed multiple times. This provides (and requires) a clean separation between

the activities that modify the persistent state of your system and the activities that generate what is

displayed to the user.

Spring Web Flow

Spring Web Flow (SWF) aims to be the best solution for the management of web application page

flow.

SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and

Portlet environments. If you have a business process (or processes) that would benefit from a

conversational model as opposed to a purely request model, then SWF may be the solution.

SWF allows you to capture logical page flows as self-contained modules that are reusable in

different situations, and as such is ideal for building web application modules that guide the user

through controlled navigations that drive business processes.

For more information about SWF, consult the Spring Web Flow website.

The dual phases of portlet requests are one of the real strengths of the JSR-168 specification. For

example, dynamic search results can be updated routinely on the display without the user explicitly

rerunning the search. Most other portlet MVC frameworks attempt to completely hide the two phases

from the developer and make it look as much like traditional servlet development as possible - we think

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 546

this approach removes one of the main benefits of using portlets. So, the separation of the two phases is

preserved throughout the Spring Portlet MVC framework. The primary manifestation of this approach is

that where the servlet version of the MVC classes will have one method that deals with the request, the

portlet version of the MVC classes will have two methods that deal with the request: one for the action

phase and one for the render phase. For example, where the servlet version of AbstractController

has the handleRequestInternal(..) method, the portlet version of AbstractController has

handleActionRequestInternal(..) and handleRenderRequestInternal(..) methods.

The framework is designed around a DispatcherPortlet that dispatches requests to handlers,

with configurable handler mappings and view resolution, just as the DispatcherServlet in the web

framework does. File upload is also supported in the same way.

Locale resolution and theme resolution are not supported in Portlet MVC - these areas are in the purview

of the portal/portlet container and are not appropriate at the Spring level. However, all mechanisms in

Spring that depend on the locale (such as internationalization of messages) will still function properly

because DispatcherPortlet exposes the current locale in the same way as DispatcherServlet.

Controllers - The C in MVC

The default handler is still a very simple Controller interface, offering just two methods:

•void handleActionRequest(request,response)

•ModelAndView handleRenderRequest(request,response)

The framework also includes most of the same controller implementation hierarchy, such as

AbstractController, SimpleFormController, and so on. Data binding, command object usage,

model handling, and view resolution are all the same as in the servlet framework.

Views - The V in MVC

All the view rendering capabilities of the servlet framework are used directly via a special bridge servlet

named ViewRendererServlet. By using this servlet, the portlet request is converted into a servlet

request and the view can be rendered using the entire normal servlet infrastructure. This means all the

existing renderers, such as JSP, Velocity, etc., can still be used within the portlet.

Web-scoped beans

Spring Portlet MVC supports beans whose lifecycle is scoped to the current HTTP request or HTTP

Session (both normal and global). This is not a specific feature of Spring Portlet MVC itself, but rather

of the WebApplicationContext container(s) that Spring Portlet MVC uses. These bean scopes are

described in detail in the section called “Request, session, and global session scopes”

20.2 The DispatcherPortlet

Portlet MVC is a request-driven web MVC framework, designed around a portlet that dispatches

requests to controllers and offers other functionality facilitating the development of portlet applications.

Spring’s DispatcherPortlet however, does more than just that. It is completely integrated with the

Spring ApplicationContext and allows you to use every other feature Spring has.

Like ordinary portlets, the DispatcherPortlet is declared in the portlet.xml file of your web

application:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 547

<portlet-name>sample</portlet-name>

<portlet-class>org.springframework.web.portlet.DispatcherPortlet</portlet-class>

<mime-type>text/html</mime-type>

<portlet-mode>view</portlet-mode>

</supports>

<portlet-info>

<title>Sample Portlet</title>

</portlet-info>

</portlet>

The DispatcherPortlet now needs to be configured.

In the Portlet MVC framework, each DispatcherPortlet has its own WebApplicationContext,

which inherits all the beans already defined in the Root WebApplicationContext. These inherited

beans can be overridden in the portlet-specific scope, and new scope-specific beans can be defined

local to a given portlet instance.

The framework will, on initialization of a DispatcherPortlet, look for a file named [portlet-

name]-portlet.xml in the WEB-INF directory of your web application and create the beans defined

there (overriding the definitions of any beans defined with the same name in the global scope).

The config location used by the DispatcherPortlet can be modified through a portlet initialization

parameter (see below for details).

The Spring DispatcherPortlet has a few special beans it uses, in order to be able to process

requests and render the appropriate views. These beans are included in the Spring framework and can

be configured in the WebApplicationContext, just as any other bean would be configured. Each of

those beans is described in more detail below. Right now, we’ll just mention them, just to let you know

they exist and to enable us to go on talking about the DispatcherPortlet. For most of the beans,

defaults are provided so you don’t have to worry about configuring them.

Table 20.1. Special beans in the WebApplicationContext

Expression Explanation

handler

mapping(s)

(Section 20.5, “Handler mappings”) a list of pre- and post-processors and

controllers that will be executed if they match certain criteria (for instance a

matching portlet mode specified with the controller)

controller(s) (Section 20.4, “Controllers”) the beans providing the actual functionality (or at

least, access to the functionality) as part of the MVC triad

view resolver (Section 20.6, “Views and resolving them”) capable of resolving view names to

view definitions

multipart resolver (Section 20.7, “Multipart (file upload) support”) offers functionality to process file

uploads from HTML forms

handler exception

resolver

(Section 20.8, “Handling exceptions”) offers functionality to map exceptions to

views or implement other more complex exception handling code

When a DispatcherPortlet is setup for use and a request comes in for that specific

DispatcherPortlet, it starts processing the request. The list below describes the complete process

a request goes through if handled by a DispatcherPortlet:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 548

1. The locale returned by PortletRequest.getLocale() is bound to the request to let elements

in the process resolve the locale to use when processing the request (rendering the view, preparing

data, etc.).

2. If a multipart resolver is specified and this is an ActionRequest, the request is inspected for

multiparts and if they are found, it is wrapped in a MultipartActionRequest for further processing

by other elements in the process. (See Section 20.7, “Multipart (file upload) support” for further

information about multipart handling).

3. An appropriate handler is searched for. If a handler is found, the execution chain associated with the

handler (pre-processors, post-processors, controllers) will be executed in order to prepare a model.

4. If a model is returned, the view is rendered, using the view resolver that has been configured with the

WebApplicationContext. If no model is returned (which could be due to a pre- or post-processor

intercepting the request, for example, for security reasons), no view is rendered, since the request

could already have been fulfilled.

Exceptions that are thrown during processing of the request get picked up by any of the handler

exception resolvers that are declared in the WebApplicationContext. Using these exception

resolvers you can define custom behavior in case such exceptions get thrown.

You can customize Spring’s DispatcherPortlet by adding context parameters in the portlet.xml

file or portlet init-parameters. The possibilities are listed below.

Table 20.2. DispatcherPortlet initialization parameters

Parameter Explanation

contextClass Class that implements WebApplicationContext, which will be used to

instantiate the context used by this portlet. If this parameter isn’t specified, the

XmlPortletApplicationContext will be used.

contextConfigLocationString which is passed to the context instance (specified by contextClass)

to indicate where context(s) can be found. The String is potentially split up into

multiple Strings (using a comma as a delimiter) to support multiple contexts (in

case of multiple context locations, for beans that are defined twice, the latest

takes precedence).

namespace The namespace of the WebApplicationContext. Defaults to [portlet-

name]-portlet.

viewRendererUrlThe URL at which DispatcherPortlet can access an instance of

ViewRendererServlet (see Section 20.3, “The ViewRendererServlet”).

20.3 The ViewRendererServlet

The rendering process in Portlet MVC is a bit more complex than in Web MVC. In order to reuse all the

view technologies from Spring Web MVC, we must convert the PortletRequest / PortletResponse

to HttpServletRequest / HttpServletResponse and then call the render method of the

View. To do this, DispatcherPortlet uses a special servlet that exists for just this purpose: the

ViewRendererServlet.

In order for DispatcherPortlet rendering to work, you must declare an instance of the

ViewRendererServlet in the web.xml file for your web application as follows:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 549

<servlet-name>ViewRendererServlet</servlet-name>

<servlet-class>org.springframework.web.servlet.ViewRendererServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>ViewRendererServlet</servlet-name>

<url-pattern>/WEB-INF/servlet/view</url-pattern>

</servlet-mapping>

To perform the actual rendering, DispatcherPortlet does the following:

1. Binds the WebApplicationContext to the request as an attribute under the same

WEB_APPLICATION_CONTEXT_ATTRIBUTE key that DispatcherServlet uses.

2. Binds the Model and View objects to the request to make them available to the

ViewRendererServlet.

3. Constructs a PortletRequestDispatcher and performs an include using the /WEB- INF/

servlet/view URL that is mapped to the ViewRendererServlet.

The ViewRendererServlet is then able to call the render method on the View with the appropriate

arguments.

The actual URL for the ViewRendererServlet can be changed using DispatcherPortlet's

viewRendererUrl configuration parameter.

20.4 Controllers

The controllers in Portlet MVC are very similar to the Web MVC Controllers, and porting code from one

to the other should be simple.

The basis for the Portlet MVC controller architecture is the

org.springframework.web.portlet.mvc.Controller interface, which is listed below.

public interface Controller {

/**

* Process the render request and return a ModelAndView object which the

* DispatcherPortlet will render.

ModelAndView handleRenderRequest(RenderRequest request,

RenderResponse response) throws Exception;

/**

* Process the action request. There is nothing to return.

void handleActionRequest(ActionRequest request,

ActionResponse response) throws Exception;

}

As you can see, the Portlet Controller interface requires two methods that handle the two phases

of a portlet request: the action request and the render request. The action phase should be capable

of handling an action request, and the render phase should be capable of handling a render request

and returning an appropriate model and view. While the Controller interface is quite abstract, Spring

Portlet MVC offers several controllers that already contain a lot of the functionality you might need;

most of these are very similar to controllers from Spring Web MVC. The Controller interface just

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 550

defines the most common functionality required of every controller: handling an action request, handling

a render request, and returning a model and a view.

AbstractController and PortletContentGenerator

Of course, just a Controller interface isn’t enough. To provide a basic infrastructure, all of Spring

Portlet MVC’s Controllers inherit from AbstractController, a class offering access to Spring’s

ApplicationContext and control over caching.

Table 20.3. Features offered by the AbstractController

Parameter Explanation

requireSession Indicates whether or not this Controller requires a session to do its

work. This feature is offered to all controllers. If a session is not present

when such a controller receives a request, the user is informed using a

SessionRequiredException.

synchronizeSessionUse this if you want handling by this controller to be synchronized

on the user’s session. To be more specific, the extending controller

will override the handleRenderRequestInternal(..) and

handleActionRequestInternal(..) methods, which will be synchronized

on the user’s session if you specify this variable.

renderWhenMinimizedIf you want your controller to actually render the view when the portlet is in a

minimized state, set this to true. By default, this is set to false so that portlets

that are in a minimized state don’t display any content.

cacheSeconds When you want a controller to override the default cache expiration defined for

the portlet, specify a positive integer here. By default it is set to -1, which does

not change the default caching. Setting it to 0 will ensure the result is never

cached.

The requireSession and cacheSeconds properties are declared on the

PortletContentGenerator class, which is the superclass of AbstractController) but are

included here for completeness.

When using the AbstractController as a base class for your controllers (which is not recommended

since there are a lot of other controllers that might already do the job for you) you only have

to override either the handleActionRequestInternal(ActionRequest, ActionResponse)

method or the handleRenderRequestInternal(RenderRequest, RenderResponse) method

(or both), implement your logic, and return a ModelAndView object (in the case of

handleRenderRequestInternal).

The default implementations of both handleActionRequestInternal(..) and

handleRenderRequestInternal(..) throw a PortletException. This is consistent with the

behavior of GenericPortlet from the JSR- 168 Specification API. So you only need to override the

method that your controller is intended to handle.

Here is short example consisting of a class and a declaration in the web application context.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 551

package samples;

import javax.portlet.RenderRequest;

import javax.portlet.RenderResponse;

import org.springframework.web.portlet.mvc.AbstractController;

import org.springframework.web.portlet.ModelAndView;

public class SampleController extends AbstractController {

public ModelAndView handleRenderRequestInternal(RenderRequest request, RenderResponse response) {

ModelAndView mav = new ModelAndView("foo");

mav.addObject("message", "Hello World!");

return mav;

}

</bean>

The class above and the declaration in the web application context is all you need besides setting up a

handler mapping (see Section 20.5, “Handler mappings”) to get this very simple controller working.

Other simple controllers

Although you can extend AbstractController, Spring Portlet MVC provides a number of concrete

implementations which offer functionality that is commonly used in simple MVC applications.

The ParameterizableViewController is basically the same as the example above, except for the

fact that you can specify the view name that it will return in the web application context (no need to

hard-code the view name).

The PortletModeNameViewController uses the current mode of the portlet as the view name. So,

if your portlet is in View mode (i.e. PortletMode.VIEW) then it uses "view" as the view name.

Command Controllers

Spring Portlet MVC has the exact same hierarchy of command controllers as Spring Web MVC. They

provide a way to interact with data objects and dynamically bind parameters from the PortletRequest

to the data object specified. Your data objects don’t have to implement a framework-specific interface,

so you can directly manipulate your persistent objects if you desire. Let’s examine what command

controllers are available, to get an overview of what you can do with them:

•AbstractCommandController - a command controller you can use to create your own command

controller, capable of binding request parameters to a data object you specify. This class does not

offer form functionality, it does however offer validation features and lets you specify in the controller

itself what to do with the command object that has been filled with the parameters from the request.

•AbstractFormController - an abstract controller offering form submission support. Using this

controller you can model forms and populate them using a command object you retrieve in the

controller. After a user has filled the form, AbstractFormController binds the fields, validates,

and hands the object back to the controller to take appropriate action. Supported features are: invalid

form submission (resubmission), validation, and normal form workflow. You implement methods to

determine which views are used for form presentation and success. Use this controller if you need

forms, but don’t want to specify what views you’re going to show the user in the application context.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 552

•SimpleFormController - a concrete AbstractFormController that provides even more

support when creating a form with a corresponding command object. The SimpleFormController

lets you specify a command object, a viewname for the form, a viewname for the page you want to

show the user when form submission has succeeded, and more.

•AbstractWizardFormController— a concrete AbstractFormController that provides a

wizard-style interface for editing the contents of a command object across multiple display pages.

Supports multiple user actions: finish, cancel, or page change, all of which are easily specified in

request parameters from the view.

These command controllers are quite powerful, but they do require a detailed understanding of how

they operate in order to use them efficiently. Carefully review the javadocs for this entire hierarchy and

then look at some sample implementations before you start using them.

PortletWrappingController

Instead of developing new controllers, it is possible to use existing portlets and map requests to them

from a DispatcherPortlet. Using the PortletWrappingController, you can instantiate an

existing Portlet as a Controller as follows:

<value>config=/WEB-INF/my-portlet-config.xml</value>

</property>

</bean>

This can be very valuable since you can then use interceptors to pre-process and post-process requests

going to these portlets. Since JSR-168 does not support any kind of filter mechanism, this is quite handy.

For example, this can be used to wrap the Hibernate OpenSessionInViewInterceptor around a

MyFaces JSF Portlet.

20.5 Handler mappings

Using a handler mapping you can map incoming portlet requests to appropriate handlers. There are

some handler mappings you can use out of the box, for example, the PortletModeHandlerMapping,

but let’s first examine the general concept of a HandlerMapping.

Note: We are intentionally using the term "Handler" here instead of "Controller". DispatcherPortlet

is designed to be used with other ways to process requests than just Spring Portlet MVC’s own

Controllers. A Handler is any Object that can handle portlet requests. Controllers are an example of

Handlers, and they are of course the default. To use some other framework with DispatcherPortlet,

a corresponding implementation of HandlerAdapter is all that is needed.

The functionality a basic HandlerMapping provides is the delivering of a HandlerExecutionChain,

which must contain the handler that matches the incoming request, and may also contain a list of handler

interceptors that are applied to the request. When a request comes in, the DispatcherPortlet will

hand it over to the handler mapping to let it inspect the request and come up with an appropriate

HandlerExecutionChain. Then the DispatcherPortlet will execute the handler and interceptors

in the chain (if any). These concepts are all exactly the same as in Spring Web MVC.

The concept of configurable handler mappings that can optionally contain interceptors (executed before

or after the actual handler was executed, or both) is extremely powerful. A lot of supporting functionality

can be built into a custom HandlerMapping. Think of a custom handler mapping that chooses a handler

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 553

not only based on the portlet mode of the request coming in, but also on a specific state of the session

associated with the request.

In Spring Web MVC, handler mappings are commonly based on URLs. Since there is really no such

thing as a URL within a Portlet, we must use other mechanisms to control mappings. The two most

common are the portlet mode and a request parameter, but anything available to the portlet request

can be used in a custom handler mapping.

The rest of this section describes three of Spring Portlet MVC’s most commonly used handler mappings.

They all extend AbstractHandlerMapping and share the following properties:

•interceptors: The list of interceptors to use. HandlerInterceptors are discussed in the section

called “Adding HandlerInterceptors”.

•defaultHandler: The default handler to use, when this handler mapping does not result in a

matching handler.

•order: Based on the value of the order property (see the org.springframework.core.Ordered

interface), Spring will sort all handler mappings available in the context and apply the first matching

handler.

•lazyInitHandlers: Allows for lazy initialization of singleton handlers (prototype handlers are

always lazily initialized). Default value is false. This property is directly implemented in the three

concrete Handlers.

PortletModeHandlerMapping

This is a simple handler mapping that maps incoming requests based on the current mode of the portlet

(e.g. view, edit, help). An example:

<map>

</map>

</property>

</bean>

ParameterHandlerMapping

If we need to navigate around to multiple controllers without changing portlet mode, the simplest way to

do this is with a request parameter that is used as the key to control the mapping.

ParameterHandlerMapping uses the value of a specific request parameter to control the mapping.

The default name of the parameter is 'action', but can be changed using the 'parameterName'

property.

The bean configuration for this mapping will look something like this:

<map>

</map>

</property>

</bean>

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 554

PortletModeParameterHandlerMapping

The most powerful built-in handler mapping, PortletModeParameterHandlerMapping combines

the capabilities of the two previous ones to allow different navigation within each portlet mode.

Again the default name of the parameter is "action", but can be changed using the parameterName

property.

By default, the same parameter value may not be used in two different portlet modes. This is so that

if the portal itself changes the portlet mode, the request will no longer be valid in the mapping. This

behavior can be changed by setting the allowDupParameters property to true. However, this is not

recommended.

The bean configuration for this mapping will look something like this:

<map>

<map>

</map>

</entry>

<map>

</map>

</entry>

</map>

</property>

</bean>

This mapping can be chained ahead of a PortletModeHandlerMapping, which can then provide

defaults for each mode and an overall default as well.

Adding HandlerInterceptors

Spring’s handler mapping mechanism has a notion of handler interceptors, which can be extremely

useful when you want to apply specific functionality to certain requests, for example, checking for a

principal. Again Spring Portlet MVC implements these concepts in the same way as Web MVC.

Interceptors located in the handler mapping must implement HandlerInterceptor from the

org.springframework.web.portlet package. Just like the servlet version, this interface defines

three methods: one that will be called before the actual handler will be executed ( preHandle), one

that will be called after the handler is executed ( postHandle), and one that is called after the complete

request has finished ( afterCompletion). These three methods should provide enough flexibility to

do all kinds of pre- and post- processing.

The preHandle method returns a boolean value. You can use this method to break or continue the

processing of the execution chain. When this method returns true, the handler execution chain will

continue. When it returns false, the DispatcherPortlet assumes the interceptor itself has taken

care of requests (and, for example, rendered an appropriate view) and does not continue executing the

other interceptors and the actual handler in the execution chain.

The postHandle method is only called on a RenderRequest. The preHandle and

afterCompletion methods are called on both an ActionRequest and a RenderRequest. If you

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 555

need to execute logic in these methods for just one type of request, be sure to check what kind of

request it is before processing it.

HandlerInterceptorAdapter

As with the servlet package, the portlet package has a concrete implementation of

HandlerInterceptor called HandlerInterceptorAdapter. This class has empty versions of all

the methods so that you can inherit from this class and implement just one or two methods when that

is all you need.

ParameterMappingInterceptor

The portlet package also has a concrete interceptor named ParameterMappingInterceptor

that is meant to be used directly with ParameterHandlerMapping and

PortletModeParameterHandlerMapping. This interceptor will cause the parameter that is

being used to control the mapping to be forwarded from an ActionRequest to the subsequent

RenderRequest. This will help ensure that the RenderRequest is mapped to the same Handler as

the ActionRequest. This is done in the preHandle method of the interceptor, so you can still modify

the parameter value in your handler to change where the RenderRequest will be mapped.

Be aware that this interceptor is calling setRenderParameter on the ActionResponse, which

means that you cannot call sendRedirect in your handler when using this interceptor. If you need to

do external redirects then you will either need to forward the mapping parameter manually or write a

different interceptor to handle this for you.

20.6 Views and resolving them

As mentioned previously, Spring Portlet MVC directly reuses all the view technologies from Spring

Web MVC. This includes not only the various View implementations themselves, but also the

ViewResolver implementations. For more information, refer to Chapter 18, View technologies and

Section 17.5, “Resolving views” respectively.

A few items on using the existing View and ViewResolver implementations are worth mentioning:

• Most portals expect the result of rendering a portlet to be an HTML fragment. So, things like JSP/

JSTL, Velocity, FreeMarker, and XSLT all make sense. But it is unlikely that views that return other

document types will make any sense in a portlet context.

• There is no such thing as an HTTP redirect from within a portlet (the sendRedirect(..) method

of ActionResponse cannot be used to stay within the portal). So, RedirectView and use of the

'redirect:' prefix will not work correctly from within Portlet MVC.

• It may be possible to use the 'forward:' prefix from within Portlet MVC. However, remember that

since you are in a portlet, you have no idea what the current URL looks like. This means you cannot

use a relative URL to access other resources in your web application and that you will have to use

an absolute URL.

Also, for JSP development, the new Spring Taglib and the new Spring Form Taglib both work in portlet

views in exactly the same way that they work in servlet views.

20.7 Multipart (file upload) support

Spring Portlet MVC has built-in multipart support to handle file uploads in

portlet applications, just like Web MVC does. The design for the multipart

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 556

support is done with pluggable PortletMultipartResolver objects, defined in

the org.springframework.web.portlet.multipart package. Spring provides a

PortletMultipartResolver for use with Commons FileUpload. How uploading files is supported

will be described in the rest of this section.

By default, no multipart handling will be done by Spring Portlet MVC, as some developers will want to

handle multiparts themselves. You will have to enable it yourself by adding a multipart resolver to the

web application’s context. After you have done that, DispatcherPortlet will inspect each request

to see if it contains a multipart. If no multipart is found, the request will continue as expected. However,

if a multipart is found in the request, the PortletMultipartResolver that has been declared in

your context will be used. After that, the multipart attribute in your request will be treated like any other

attribute.

Note

Any configured PortletMultipartResolver bean must have the following id (or name):

" portletMultipartResolver". If you have defined your PortletMultipartResolver

with any other name, then the DispatcherPortlet will not find your

PortletMultipartResolver, and consequently no multipart support will be in effect.

Using the PortletMultipartResolver

The following example shows how to use the CommonsPortletMultipartResolver:

<bean id="portletMultipartResolver"

class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver">

</bean>

Of course you also need to put the appropriate jars in your classpath for the multipart resolver to work.

In the case of the CommonsMultipartResolver, you need to use commons-fileupload.jar. Be

sure to use at least version 1.1 of Commons FileUpload as previous versions do not support JSR-168

Portlet applications.

Now that you have seen how to set Portlet MVC up to handle multipart requests, let’s talk about how to

actually use it. When DispatcherPortlet detects a multipart request, it activates the resolver that

has been declared in your context and hands over the request. What the resolver then does is wrap the

current ActionRequest in a MultipartActionRequest that has support for multipart file uploads.

Using the MultipartActionRequest you can get information about the multiparts contained by this

request and actually get access to the multipart files themselves in your controllers.

Note that you can only receive multipart file uploads as part of an ActionRequest, not as part of a

RenderRequest.

Handling a file upload in a form

After the PortletMultipartResolver has finished doing its job, the request will be processed like

any other. To use the PortletMultipartResolver, create a form with an upload field (see example

below), then let Spring bind the file onto your form (backing object). To actually let the user upload a

file, we have to create a (JSP/HTML) form:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 557

<h1>Please upload a file</h1>

<form method="post" action="<portlet:actionURL/>" enctype="multipart/form-data">

</form>

As you can see, we’ve created a field named "file" that matches the property of the bean that holds

the byte[] array. Furthermore we’ve added the encoding attribute ( enctype="multipart/form-

data"), which is necessary to let the browser know how to encode the multipart fields (do not forget

this!).

Just as with any other property that’s not automagically convertible to a string or primitive type,

to be able to put binary data in your objects you have to register a custom editor with the

PortletRequestDataBinder. There are a couple of editors available for handling files and setting

the results on an object. There’s a StringMultipartFileEditor capable of converting files to

Strings (using a user-defined character set), and there is a ByteArrayMultipartFileEditor which

converts files to byte arrays. They function analogous to the CustomDateEditor.

So, to be able to upload files using a form, declare the resolver, a mapping to a controller that will

process the bean, and the controller itself.

<bean id="portletMultipartResolver"

class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver"/>

<map>

</map>

</property>

</bean>

</bean>

After that, create the controller and the actual class to hold the file property.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 558

public class FileUploadController extends SimpleFormController {

public void onSubmitAction(ActionRequest request, ActionResponse response,

Object command, BindException errors) throws Exception {

// cast the bean

FileUploadBean bean = (FileUploadBean) command;

// let's see if there's content there

byte[] file = bean.getFile();

if (file == null) {

// hmm, that's strange, the user did not upload anything

}

// do something with the file here

}

protected void initBinder(PortletRequest request,

PortletRequestDataBinder binder) throws Exception {

// to actually be able to convert Multipart instance to byte[]

// we have to register a custom editor

binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor());

// now Spring knows how to handle multipart object and convert

}

public class FileUploadBean {

private byte[] file;

public void setFile(byte[] file) {

this.file = file;

}

public byte[] getFile() {

return file;

}

As you can see, the FileUploadBean has a property of type byte[] that holds the file. The controller

registers a custom editor to let Spring know how to actually convert the multipart objects the resolver has

found to properties specified by the bean. In this example, nothing is done with the byte[] property of

the bean itself, but in practice you can do whatever you want (save it in a database, mail it to somebody,

etc).

An equivalent example in which a file is bound straight to a String-typed property on a form backing

object might look like this:

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 559

public class FileUploadController extends SimpleFormController {

public void onSubmitAction(ActionRequest request, ActionResponse response,

Object command, BindException errors) throws Exception {

// cast the bean

FileUploadBean bean = (FileUploadBean) command;

// let's see if there's content there

String file = bean.getFile();

if (file == null) {

// hmm, that's strange, the user did not upload anything

}

// do something with the file here

}

protected void initBinder(PortletRequest request,

PortletRequestDataBinder binder) throws Exception {

// to actually be able to convert Multipart instance to a String

// we have to register a custom editor

binder.registerCustomEditor(String.class, new StringMultipartFileEditor());

// now Spring knows how to handle multipart objects and convert

}

public class FileUploadBean {

private String file;

public void setFile(String file) {

this.file = file;

}

public String getFile() {

return file;

}

Of course, this last example only makes (logical) sense in the context of uploading a plain text file (it

wouldn’t work so well in the case of uploading an image file).

The third (and final) option is where one binds directly to a MultipartFile property declared on the

(form backing) object’s class. In this case one does not need to register any custom property editor

because there is no type conversion to be performed.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 560

public class FileUploadController extends SimpleFormController {

public void onSubmitAction(ActionRequest request, ActionResponse response,

Object command, BindException errors) throws Exception {

// cast the bean

FileUploadBean bean = (FileUploadBean) command;

// let's see if there's content there

MultipartFile file = bean.getFile();

if (file == null) {

// hmm, that's strange, the user did not upload anything

}

// do something with the file here

}

public class FileUploadBean {

private MultipartFile file;

public void setFile(MultipartFile file) {

this.file = file;

}

public MultipartFile getFile() {

return file;

}

20.8 Handling exceptions

Just like Servlet MVC, Portlet MVC provides HandlerExceptionResolvers to ease the pain of

unexpected exceptions that occur while your request is being processed by a handler that matched the

request. Portlet MVC also provides a portlet-specific, concrete SimpleMappingExceptionResolver

that enables you to take the class name of any exception that might be thrown and map it to a view name.

20.9 Annotation-based controller configuration

Spring 2.5 introduced an annotation-based programming model for MVC controllers, using annotations

such as @RequestMapping, @RequestParam, @ModelAttribute, etc. This annotation support is

available for both Servlet MVC and Portlet MVC. Controllers implemented in this style do not have to

extend specific base classes or implement specific interfaces. Furthermore, they do not usually have

direct dependencies on Servlet or Portlet API’s, although they can easily get access to Servlet or Portlet

facilities if desired.

The following sections document these annotations and how they are most commonly used in a Portlet

environment.

Setting up the dispatcher for annotation support

`@RequestMapping` will only be processed if a corresponding HandlerMapping (for type level

annotations) and/or HandlerAdapter (for method level annotations) is present in the dispatcher. This

is the case by default in both DispatcherServlet and DispatcherPortlet.

However, if you are defining custom HandlerMappings or HandlerAdapters, then you

need to make sure that a corresponding custom DefaultAnnotationHandlerMapping and/

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 561

or AnnotationMethodHandlerAdapter is defined as well - provided that you intend to use

@RequestMapping.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd">

// ... (controller bean definitions) ...

</beans>

Defining a DefaultAnnotationHandlerMapping and/or AnnotationMethodHandlerAdapter

explicitly also makes sense if you would like to customize the mapping strategy, e.g. specifying a custom

WebBindingInitializer (see below).

Defining a controller with @Controller

The @Controller annotation indicates that a particular class serves the role of a controller. There is

no need to extend any controller base class or reference the Portlet API. You are of course still able to

reference Portlet-specific features if you need to.

The basic purpose of the @Controller annotation is to act as a stereotype for the annotated class,

indicating its role. The dispatcher will scan such annotated classes for mapped methods, detecting

@RequestMapping annotations (see the next section).

Annotated controller beans may be defined explicitly, using a standard Spring bean definition in the

dispatcher’s context. However, the @Controller stereotype also allows for autodetection, aligned with

Spring 2.5’s general support for detecting component classes in the classpath and auto-registering bean

definitions for them.

To enable autodetection of such annotated controllers, you have to add component scanning to your

configuration. This is easily achieved by using the spring-context schema as shown in the following

XML snippet:

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:p="http://www.springframework.org/schema/p"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="

http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd">

<context:component-scan base-package="org.springframework.samples.petportal.portlet"/>

// ...

</beans>

Mapping requests with @RequestMapping

The @RequestMapping annotation is used to map portlet modes like VIEW/EDIT onto an entire class

or a particular handler method. Typically the type-level annotation maps a specific mode (or mode

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 562

plus parameter condition) onto a form controller, with additional method-level annotations narrowing the

primary mapping for specific portlet request parameters.

Tip

@RequestMapping at the type level may be used for plain implementations of the Controller

interface as well. In this case, the request processing code would follow the traditional

handle(Action|Render)Request signature, while the controller’s mapping would be

expressed through an @RequestMapping annotation. This works for pre-built Controller base

classes, such as SimpleFormController, too.

In the following discussion, we’ll focus on controllers that are based on annotated handler

methods.

The following is an example of a form controller from the PetPortal sample application using this

annotation:

@Controller

@RequestMapping("EDIT")

@SessionAttributes("site")

public class PetSitesEditController {

private Properties petSites;

public void setPetSites(Properties petSites) {

this.petSites = petSites;

}

@ModelAttribute("petSites")

public Properties getPetSites() {

return this.petSites;

}

@RequestMapping // default (action=list)

public String showPetSites() {

return "petSitesEdit";

}

@RequestMapping(params = "action=add") // render phase

public String showSiteForm(Model model) {

// Used for the initial form as well as for redisplaying with errors.

if (!model.containsAttribute("site")) {

model.addAttribute("site", new PetSite());

}

return "petSitesAdd";

}

@RequestMapping(params = "action=add") // action phase

public void populateSite(@ModelAttribute("site") PetSite petSite,

BindingResult result, SessionStatus status, ActionResponse response) {

new PetSiteValidator().validate(petSite, result);

if (!result.hasErrors()) {

this.petSites.put(petSite.getName(), petSite.getUrl());

status.setComplete();

response.setRenderParameter("action", "list");

}

@RequestMapping(params = "action=delete")

public void removeSite(@RequestParam("site") String site, ActionResponse response) {

this.petSites.remove(site);

response.setRenderParameter("action", "list");

}

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 563

Supported handler method arguments

Handler methods which are annotated with @RequestMapping are allowed to have very flexible

signatures. They may have arguments of the following types, in arbitrary order (except for validation

results, which need to follow right after the corresponding command object, if desired):

• Request and/or response objects (Portlet API). You may choose any specific request/response type,

e.g. PortletRequest / ActionRequest / RenderRequest. An explicitly declared action/render argument

is also used for mapping specific request types onto a handler method (in case of no other information

given that differentiates between action and render requests).

• Session object (Portlet API): of type PortletSession. An argument of this type will enforce the presence

of a corresponding session. As a consequence, such an argument will never be null.

•org.springframework.web.context.request.WebRequest or

org.springframework.web.context.request.NativeWebRequest. Allows for generic

request parameter access as well as request/session attribute access, without ties to the native

Servlet/Portlet API.

•java.util.Locale for the current request locale (the portal locale in a Portlet environment).

•java.util.TimeZone / java.time.ZoneId for the current request time zone.

•java.io.InputStream / java.io.Reader for access to the request’s content. This will be the

raw InputStream/Reader as exposed by the Portlet API.

•java.io.OutputStream / java.io.Writer for generating the response’s content. This will be

the raw OutputStream/Writer as exposed by the Portlet API.

•@RequestParam annotated parameters for access to specific Portlet request parameters. Parameter

values will be converted to the declared method argument type.

•java.util.Map / org.springframework.ui.Model /

org.springframework.ui.ModelMap for enriching the implicit model that will be exposed to the

web view.

• Command/form objects to bind parameters to: as bean properties or fields, with customizable

type conversion, depending on @InitBinder methods and/or the HandlerAdapter configuration -

see the " webBindingInitializer" property on AnnotationMethodHandlerAdapter. Such

command objects along with their validation results will be exposed as model attributes, by default

using the non-qualified command class name in property notation (e.g. "orderAddress" for type

"mypackage.OrderAddress"). Specify a parameter-level ModelAttribute annotation for declaring

a specific model attribute name.

•org.springframework.validation.Errors /

org.springframework.validation.BindingResult validation results for a preceding

command/form object (the immediate preceding argument).

•org.springframework.web.bind.support.SessionStatus status handle for marking form

processing as complete (triggering the cleanup of session attributes that have been indicated by the

@SessionAttributes annotation at the handler type level).

The following return types are supported for handler methods:

• A ModelAndView object, with the model implicitly enriched with command objects and the results of

@ModelAttribute annotated reference data accessor methods.

Spring Framework Reference Documentation

4.1.0.RELEASE Spring Framework 564